Add release action

Only PA and PB implemented, not tested

.gitea/workflows/build.yaml

@@ -0,0 +1,36 @@
+name: Build and Test
+
+on:
+  push:
+    branches:
+      - master
+  pull_request:
+  workflow_dispatch:
+
+jobs:
+  build:
+    runs-on: ubuntu-latest
+    container:
+      image: catthehacker/ubuntu:act-latest
+    steps:
+      - name: Checkout code
+        uses: actions/checkout@v4
+
+      - name: Setup JDK
+        uses: actions/setup-java@v6
+        with:
+          distribution: temurin
+          java-version: '21'
+          #cache: maven
+
+      - name: Install Maven
+        run: apt-get update && apt-get install -y maven
+
+      - name: Test and package
+        run: mvn -B verify
+
+      - name: Upload jar
+        uses: actions/upload-artifact@v3
+        with:
+          name: package
+          path: target/*.jar

.gitea/workflows/release.yaml

@@ -0,0 +1,33 @@
+name: Release
+
+on:
+  push:
+    tags:
+      - 'v*'
+
+jobs:
+  release:
+    runs-on: ubuntu-latest
+    container:
+      image: catthehacker/ubuntu:act-latest
+    steps:
+      - name: Checkout code
+        uses: actions/checkout@v4
+
+      - name: Setup JDK
+        uses: actions/setup-java@v6
+        with:
+          distribution: temurin
+          java-version: '21'
+
+      - name: Install Maven
+        run: apt-get update && apt-get install -y maven
+
+      - name: Package
+        run: mvn -B verify
+
+      - name: Create release
+        uses: https://gitea.com/actions/gitea-release-action@v1
+        with:
+          files: |-
+            target/symon*.jar

.gitignore

@@ -1,6 +1,8 @@
 *~
+*.jar
 *#
 target
 .DS_Store
 .idea
 symon.iml
+/dependency-reduced-pom.xml

.settings/org.eclipse.core.resources.prefs

@@ -0,0 +1,5 @@
+eclipse.preferences.version=1
+encoding//src/main/java=UTF-8
+encoding//src/main/resources=UTF-8
+encoding//src/test/java=UTF-8
+encoding/<project>=UTF-8

.settings/org.eclipse.jdt.core.prefs

@@ -0,0 +1,5 @@
+eclipse.preferences.version=1
+org.eclipse.jdt.core.compiler.codegen.targetPlatform=1.7
+org.eclipse.jdt.core.compiler.compliance=1.7
+org.eclipse.jdt.core.compiler.problem.forbiddenReference=warning
+org.eclipse.jdt.core.compiler.source=1.7

.settings/org.eclipse.m2e.core.prefs

@@ -0,0 +1,4 @@
+activeProfiles=
+eclipse.preferences.version=1
+resolveWorkspaceProjects=true
+version=1

COPYING

@@ -1,6 +1,6 @@
 The MIT License
 
-Copyright (c) 2008-2013 Seth J. Morabito <web@loomcom.com>
+Copyright (c) 2008-2014 Seth J. Morabito <web@loomcom.com>
 
 Permission is hereby granted, free of charge, to any person obtaining
 a copy of this software and associated documentation files (the

README.md

@@ -1,18 +1,13 @@
-SYMON - A 6502 System Simulator
+kSYMON - A 6502 System Simulator
 ===============================
 
-**NOTE: THIS SOFTWARE IS UNDER ACTIVE DEVELOPMENT. Feedback is welcome!**
+**Version:** 1.5.1k
 
-**Version:** 0.9.0.1
-
-**Last Updated:** 29 December, 2013
-
-Copyright (c) 2013 Seth J. Morabito <web@loomcom.com>
+**Last Updated:** 24 September, 2026
 
 See the file COPYING for license.
 
-
-![Symon Simulator in Action] (https://github.com/sethm/symon/raw/master/screenshots/full.jpg)
+![Symon Simulator in Action](https://codeberg.org/sethm/symon/raw/master/screenshots/full.jpg)
 
 ## 1.0 About
 
@@ -21,82 +16,148 @@ Technologies 6502 microprocessor and compatibles. Symon is implemented
 in Java. Its core goals are accuracy, ease of development, clear
 documentation, and extensive test suites for validating correctness.
 
-Symon simulates a complete system with a 1 MHz NMOS 6502, 32KB of RAM,
-16KB of ROM, a 6551 ACIA, a 6522 VIA, and a 6545 CRTC.
+Symon simulates a complete system with a 1 MHz NMOS 6502 or CMOS
+65C02, 32KB of RAM, 16KB of ROM, a MOS 6551 or Motorola 6850 ACIA, a
+MOS 6522 VIA, and an experimental 6545 CRTC.
 
 Symon has extensive unit tests to verify correctness, and fully passes
 Klaus Dormann's 6502 Functional Test Suite as of version 0.8.2
-(See [this thread on the 6502.org Forums] (http://forum.6502.org/viewtopic.php?f=2&t=2241)
+(See [this thread on the 6502.org Forums](http://forum.6502.org/viewtopic.php?f=2&t=2241)
 for more information about this functional test suite).
 
+Symon is under active maintenance. Feedback and patches are always
+welcome.
+
 ## 2.0 Requirements
 
-  - Java 1.5 or higher
-  - Maven 2.0.x or higher (for building from source)
+  - Java 10 or higher
+  - Maven 3.0.x or higher (for building from source)
   - JUnit 4 or higher (for testing)
 
 ## 3.0 Features
 
-### 3.1 Memory Map
+Symon can simulate multiple 6502 based architectures. At present, four
+machines are implemented: Symon (the default), MULTICOMP, BenEater, and
+a "Simple" machine useful for debugging.
+
+### 3.1 Memory Maps
+
+#### 3.1.1 Symon Memory Map
 
   - `$0000`--`$7FFF`: 32KB RAM
   - `$8000`--`$800F`: 6522 VIA
-  - `$8800`--`$8803`: 6551 ACIA (Serial Console)
-  - `$9000`--`$9001`: 6545 CRTC
+  - `$8800`--`$8803`: MOS 6551 ACIA (Serial Console)
+  - `$9000`--`$9001`: MOS 6545 CRTC
   - `$C000`--`$FFFF`: 16KB ROM
 
-The CRT Controller uses memory address `$7000` as the start of Video memory.
+The CRT Controller uses memory address `$7000` as the start of Video
+memory.
+
+#### 3.1.2 MULTICOMP Memory Map
+
+  - `$0000`--`$DFFF`: 56KB RAM
+  - `$E000`--`$FFFF`: 8KB ROM
+  - `$FFD0`--`$FFD1`: Motorola 6850 ACIA
+  - `$FFD8`--`$FFDF`: Controller for SD cards
+
+### 3.1.3 Simple Memory Map
+
+  - `$0000`--`$FFFF`: 64KB RAM
+
+#### 3.1.4 BenEater Memory Map
+
+  - `$0000`--`$3FFF`: 16KB RAM
+  - `$5000`--`$5003`: MOS 6551 ACIA (Serial Console)
+  - `$6000`--`$600F`: 6522 VIA
+  - `$8000`--`$FFFF`: 16KB ROM
+
+#### 3.1.5 Mike42 Memory Map
+
+  - `$0000`--`$7FFF`: 32KB RAM
+  - `$8000`--`$800F`: 6522 VIA
+  - `$8400`--`$8403`: MOS 6551 ACIA (Serial Console)
+  - `$C000`--`$FFFF`: 16KB ROM
 
 ### 3.2 Serial Console and CPU Status
 
-![Serial Console] (https://github.com/sethm/symon/raw/master/screenshots/console.png)
+![Serial Console](https://codeberg.org/sethm/symon/raw/master/screenshots/console.png)
 
 The main window of the simulator acts as the primary Input/Output
-system through a virtual serial terminal. The terminal is attached to
-a simulated MOS 6551 ACIA, including a programmable baud rate
-generator that tries to approximate the correct "feel" of the
-programmed baud rate. (The sample Enhanced BASIC ROM image is
-programmed for 9600 baud)
+system through a virtual serial terminal. It also provides CPU status.
+Contents of the accumulator, index registers, processor status flags,
+disassembly of the instruction register, and stack pointer are all displayed.
 
-It also provides CPU status. Contents of the accumulator, index
-registers, processor status flags, disassembly of the instruction
-register, and stack pointer are all displayed.
+The terminal is attached to a simulated MOS 6551 ACIA. It behaves very much
+as described in the datasheet, with some exceptions:
 
-![Font Selection] (https://github.com/sethm/symon/raw/master/screenshots/font_selection.png)
+  - The simulated ACIA is permanently connected to the virtual terminal,
+    the Data Carrier Detect and Data Set Ready status bits always indicate
+    a connection is ready.
+  - The parity, stop-bits and bits-per-character settings are ignored. The
+    ACIA always sends and receives 8-bit characters, and parity errors
+    do not occur.
+  - The ACIA tries to honour the configured baud rate, but as a special case
+    the default "16x External Clock" rate is interpreted to mean "as fast as
+    possible" (The sample Enhanced BASIC ROM image is programmed for 9600 baud).
+  - The ACIA ignores the configured state of the Data Terminal Ready pin;
+    it is always ready to receive and transmit.
+
+For more information on the MOS 6551 ACIA and its programming model,
+see the official datasheet:
+
+  - [MOS 6551 ACIA](http://archive.6502.org/datasheets/mos_6551_acia.pdf)
+
+![Font Selection](https://codeberg.org/sethm/symon/raw/master/screenshots/font_selection.png)
 
 The console supports font sizes from 10 to 20 points.
 
-### 3.3 16 KB ROM Loading
+### 3.3 ROM Loading
 
-![ROM Loading] (https://github.com/sethm/symon/raw/master/screenshots/load_rom.png)
+![ROM Loading](https://codeberg.org/sethm/symon/raw/master/screenshots/load_rom.png)
 
-Symon can load any 16 KB (16384 bytes) ROM image from the "File"
-menu. The selected ROM will be placed in memory from locations `$C000`
-to `$FFFF`
+Symon can load any appropriately sized ROM image. The Symon
+architecture expects as 16KB (16384 byte) ROM image, while the
+MULTICOMP architecture expects an 8KB (8192 byte) ROM image. Images
+are loaded via the "Load ROM..." action in the "File" menu. The
+selected ROM file will be loaded into memory at the correct ROM base
+address.
 
 ### 3.4 Memory Window
 
-![Memory Window] (https://github.com/sethm/symon/raw/master/screenshots/memory_window.png)
+![Memory Window](https://codeberg.org/sethm/symon/raw/master/screenshots/memory_window.png)
 
 Memory contents can be viewed (and edited) one page at a time through the Memory Window.
 
 ### 3.5 Trace Log
 
-![Trace Log] (https://github.com/sethm/symon/raw/master/screenshots/trace_log.png)
+![Trace Log](https://codeberg.org/sethm/symon/raw/master/screenshots/trace_log.png)
 
-The last 20,000 execution steps are disassembled and logged to the Trace Log Window.
+The last 20,000 execution steps are disassembled and logged to the Trace Log
+Window.
 
-### 3.6 NEW - Experimental 6545 CRTC Video
+### 3.6 Simulator Speeds
 
-![Composite Video] (https://github.com/sethm/symon/raw/master/screenshots/video_window.png)
+![Speeds](https://codeberg.org/sethm/symon/raw/master/screenshots/simulator_menu.png)
 
-This feature is highly experimental. It's possible to open a video window from the "View" menu.
-This window simulates the output of a MOS 6545 CRT Controller located at address `$9000` and
-`$9001`.
+Simulated speeds may be set from 1MHz to 8MHz.
 
-By default, the 40 x 25 character display uses video memory located at base address `$7000`.
-This means that the memory from address `$7000` (28672 decimal) to `$73E8` (29672 decimal)
-is directly mapped to video.
+### 3.7 Breakpoints
+
+![Breakpoints](https://codeberg.org/sethm/symon/raw/master/screenshots/breakpoints.png)
+
+Breakpoints can be set and removed through the Breakpoints window.
+
+### 3.8 Experimental 6545 CRTC Video
+
+![Composite Video](https://codeberg.org/sethm/symon/raw/master/screenshots/video_window.png)
+
+This feature is highly experimental. It's possible to open a video window
+from the "View" menu.  This window simulates the output of a MOS 6545 CRT
+Controller located at address `$9000` and `$9001`.
+
+By default, the 40 x 25 character display uses video memory located at base
+address `$7000`.  This means that the memory from address `$7000` (28672
+decimal) to `$73E8` (29672 decimal) is directly mapped to video.
 
   - Address Register (at address `$9000`)
   - R1: Horizontal Displayed Columns
@@ -109,27 +170,29 @@ is directly mapped to video.
   - R14: Cursor Position (High Byte)
   - R15: Cursor Position (Low Byte)
 
-Although the simulation is pretty good, there are a few key differences between
-the simulated 6545 and a real 6545:
+Although the simulation is pretty good, there are a few key differences
+between the simulated 6545 and a real 6545:
 
-  - The simulated 6545 supports only the straight binary addressing mode of the real 6545,
-    and not the Row/Column addressing mode.
-  - The simulated 6545 has full 16 bit addressing, where the real 6545 has only
-    a 14-bit address bus.
-  - The simulation is done at a whole-frame level, meaning that lots of
-    6545 programming tricks that were achieved by updating the frame address
-    during vertical and horizontal sync times are not achievable. There is no way
-    (for example) to change the Display Start Address (R12 and R13) while a
-    frame is being drawn.
+  - The simulated 6545 supports only the straight binary addressing
+    mode of the real 6545, and not the Row/Column addressing mode.
+
+  - The simulated 6545 has full 16 bit addressing, where the real 6545
+    has only a 14-bit address bus.
+
+  - The simulation is done at a whole-frame level, meaning that lots
+    of 6545 programming tricks that were achieved by updating the
+    frame address during vertical and horizontal sync times are not
+    achievable.  There is no way (for example) to change the Display Start
+    Address (R12 and R13) while a frame is being drawn.
 
 For more information on the 6545 CRTC and its programming model, please see the following resources
 
-  - [CRTC 6545/6845 Information (André Fachat)] (http://6502.org/users/andre/hwinfo/crtc/index.html)
-  - [CRTC Operation (André Fachat)] (http://www.6502.org/users/andre/hwinfo/crtc/crtc.html)
-  - [MOS 6545 Datasheet (PDF)] (http://www.6502.org/users/andre/hwinfo/crtc/crtc.html)
+  - [CRTC 6545/6845 Information (André Fachat)](http://6502.org/users/andre/hwinfo/crtc/index.html)
+  - [CRTC Operation (André Fachat)](http://www.6502.org/users/andre/hwinfo/crtc/crtc.html)
+  - [MOS 6545 Datasheet (PDF)](http://www.6502.org/users/andre/hwinfo/crtc/crtc.html)
 
 
-#### 3.6.1 Example BASIC Program to test Video
+#### 3.8.1 Example BASIC Program to test Video
 
 This program will fill the video screen with all printable characters.
 
@@ -152,28 +215,57 @@ Maven will build Symon, run unit tests, and produce a jar file in the
 `target` directory containing the compiled simulator.
 
 Symon is meant to be invoked directly from the jar file. To run with
-Java 1.5 or greater, just type:
+Java 1.8 or greater, just type:
 
-    $ java -jar symon-0.9.0.jar
+    $ java -jar symon-1.2.0.jar
 
 When Symon is running, you should be presented with a simple graphical
 interface.
 
-### 4.2 ROM images
+#### 4.1.1 Command Line Options
 
-The simulator requires a 16KB ROM image loaded at address `$C000` to `$FFFF` to
-work properly. Without a ROM in memory, the simulator will not be able to
-reset, since the reset vector for the 6502 is located in this address space.
+Two command line options may be passed to the JAR file on startup,
+to specify machine type and CPU type. The options are:
 
-By default, any 16KB file named `rom.bin` that exists in the same directory
-where Symon is launched will be loaded as a ROM image. ROM images can also
-be swapped out at run-time with the "Load ROM Image..." in the File menu.
+  - `-c`,`-cpu 6502`: Use the NMOS 6502 CPU type by default.
+  - `-c`,`-cpu 65c02`: Use the CMOS 65C02 CPU type by default.
+  - `-c`,`-machine symon`: Use the **Symon** machine type by default.
+  - `-c`,`-machine multicomp`: Use the **Multicomp** machine type by default.
+  - `-m`,`-machine simple`: Use the **Simple** machine type by default.
+  - `-m`,`-machine beneater`: Use the **BenEater** machine type by default.
+  - `-r`,`-rom <file>`: Use the specified file as the ROM image.
+  - `-b`,`-brk`: Halt the simulator on a BRK instruction (default is to continue)
 
-The "samples" directory contains a ROM image named 'ehbasic.rom', containing
-Lee Davison's Enhanced 6502 BASIC. This serves as a good starting point for
-exploration.
+### 4.2 High-DPI UI scaling
 
-### 4.3 Loading A Program
+In certain environments with high-DPI (e.g. 4K) displays, the UI may
+not automatically scale and appear quite tiny. This can be fixed
+with the command line argument `-Dsun.java2d.uiScale=<factor>`,
+for example:
+
+```
+java -Dsun.java2d.uiScale=2.0 -jar symon-1.5.0.jar
+```
+
+### 4.3 ROM images
+
+The simulator requires a ROM image loaded into memory to work
+properly. Without a ROM in memory, the simulator will not be able to
+reset, since the reset vector for the 6502 is located in the ROM
+address space.
+
+ROM images can be loaded with the `-rom` argument when running
+Symon from the command line. ROM images can also be swapped out at
+run-time with the "Load ROM..." item in the File menu.
+
+The "samples" directory contains a ROM image for the Symon
+architecture named 'ehbasic.rom', containing Lee Davison's Enhanced
+6502 BASIC. This serves as a good starting point for exploration.
+
+*Note*: Presently, EhBASIC only works with the Symon machine
+ architecture, not with MULTICOMP.
+
+### 4.4 Loading A Program
 
 In addition to ROM images, programs in the form of raw binary object files can
 be loaded directly into memory from "Load Program..." in the File menu.
@@ -184,18 +276,73 @@ reset.
 
 There are two very simple sample program in the "samples" directory,
 for testing.
-  
+
 - 'echo.prg' will echo back anything typed at the console.
 
 - 'hello.prg' will continuously print "Hello, 6502 World!" to the console.
 
-### 4.4 Running
+### 4.5 Running
 
 After loading a program or ROM image, clicking "Run" will start the simulator
 running.
 
 ## 5.0 Revision History
 
+  - **1.5.0:** 30 March 2025 - Fixed a bug that caused some 6502
+    instructions to be disassembled improperly in the trace log
+    (GitHub issue #17).
+
+    Added a new "Step Over" button that allows stepping over the
+    current subroutine. This button only becomes active when the
+    next instruction is a "JSR" while stepping through execution 
+    one instruction at a time. It will continue execution until
+    the subroutine returns through a corresponding "RTS" instruction.
+    (GitHub feature request #18).
+
+  - **1.4.0:** 11 November 2023 - Adds a new machine, the Ben Eater
+    machine.  Correct handling of 6551 interrupts, and several 6551
+    bug fixes. Fixes power-on status of 6502 status register. Fixes a
+    bug with ASCII backspace character not moving the cursor
+    backwards. Finally, "halt on BRK" is no longer enabled by default,
+    but can be set at runtime or by a command line flag. Thank you to
+    Tim Allen and Chelsea Wilkinson for contributions!
+
+  - **1.3.2:** 8 March 2022 - Minor bug fixes.
+
+  - **1.3.1:** 12 October, 2019 - Add support for new command line
+    option `-cpu <type>` to specify one of `6502` or `65c02` on startup,
+    and new option `-rom <file>` to specify a ROM file to load.
+
+  - **1.3.0:** 24 February, 2018 - Adds support for 65C02 opcodes.
+
+  - **1.2.1:** 8 January, 2016 - Remove dependency on Java 8. Now
+    supports compiling and running under Java 1.7.
+
+  - **1.2.0:** 3 January, 2016 - Add symbolic disassembly to breakpoints
+    window.
+
+  - **1.1.1:** 2 January, 2016 - Minor enhancement: Allows breakpoints
+    to be added with the Enter key.
+
+  - **1.1.0:** 31 December, 2015 - Fixed delay loop to better
+    simulate various clock speeds. Added ability to select clock
+    speed at runtime. Status display now shows the next instruction
+    to be executed, instead of the last instruction executed.
+    Added support for breakpoints.
+
+  - **1.0.0:** 10 August, 2014 - Added "Simple" machine
+    implementation, pure RAM with no IO. Added Klaus Dormann's
+    6502 Functional Tests for further machine verification (these
+    tests must be run in the "Simple" machine).
+
+  - **0.9.9.1:** 27 July, 2014 - Pressing 'Control' while clicking
+    'Reset' now performs a memory clear.
+
+  - **0.9.9:** 26 July, 2014 - MULTICOMP and multi-machine support
+    contributed by Maik Merten &lt;maikmerten@googlemail.com&gt;
+
+  - **0.9.1:** 26 January, 2014 - Support for IRQ and NMI handling.
+
   - **0.9.0:** 29 December, 2013 - First pass at a 6545 CRTC simulation.
 
   - **0.8.5:** 30 March, 2013 - ASCII display for memory window.
@@ -225,42 +372,62 @@ running.
 
   - **0.1:** 20 January, 2010
 
-## 6.0 To Do
+## 6.0 Roadmap
+
+  - **1.2:** Better breakpoint support. Symbolic debugging of breakpoints.
+
+  - **2.0:** Complete rewrite of the UI in JavaFX instead of Swing. Complete
+    assembler and disassembler built in. Ability to attach source code for
+    symbolic debugging.
+
+## 7.0 To Do
 
   - Feedback (in the form of dialogs, status bar, etc).
 
-  - Better debugging tools from the UI, including breakpoints
-    and disassembly.
-
-  - More accurate timing.
-  
-  - Smarter interrupt handling.
-
   - UI needs a ton more polish.
 
   - More extensive testing.
 
   - Clean up JavaDoc.
 
-  - Implement CMOS 65C02 instructions and NMOS / CMOS mode flag.
-
   - Allow displaying ACIA status and dumping ACIA buffers, for
     debugging.
 
-## 7.0 Acknowledgements
+  - CRTC emulation is very naive. The whole frame is drawn in one
+    CPU step. This should be improved by drawing scan lines during
+    machine steps to approximate real NTSC/PAL refresh rates.
+
+  - Symbolic debugging.
+
+  - Better / correct disassembly and tracing of 65C02 and 65C816
+    instructions.
+
+## 8.0 Copyright and Acknowledgements
+
+**Copyright (c) 2008-2025 Seth J. Morabito &lt;web@loomcom.com&gt;**
+
+  - Portions Copyright (c) 2014 Maik Merten 
+    &lt;maikmerten@googlemail.com&gt;
+  - Portions Copyright (c) 2022 Tim Allen 
+    &lt;thristian@gmail.com&gt;
+  - Portions Copyright (c) 2023 Chelsea Wilkinson 
+    &lt;mail@chelseawilkinson.me&gt;
+
+Additional components used in this project are copyright their respective owners.
+
+  - Enhanced 6502 BASIC Copyright (c) Lee Davison
+  - 6502 Functional Tests Copyright (c) Klaus Dormann
+  - JTerminal Copyright (c) Graham Edgecombe
 
 This project would not have been possible without the following resources:
 
-  - [Graham Edgecombe's JTerminal project] (https://github.com/grahamedgecombe/jterminal),
-    which forms the core of Symon's console.
-
-  - [Andrew Jacobs' 6502 Pages] (http://www.obelisk.demon.co.uk/6502/), for 
+  - [Andrew Jacobs' 6502 Pages](http://obelisk.me.uk/6502/), for
     wonderfully detailed information about the 6502
 
-  - [Neil Parker's "The 6502/65C02/65C816 Instruction Set Decoded"] (http://www.llx.com/~nparker/a2/opcodes.html),
+  - [Neil Parker's "The 6502/65C02/65C816 Instruction Set Decoded"](http://www.llx.com/~nparker/a2/opcodes.html),
     for information about how instructions are coded
 
-## 8.0 Licensing
+## 9.0 Licensing
 
 Symon is free software.  It is distributed under the MIT License.
 Please see the file 'COPYING' for full details of the license.

pom.xml

@@ -1,12 +1,13 @@
-<project xmlns="http://maven.apache.org/POM/4.0.0" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
-         xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 http://maven.apache.org/maven-v4_0_0.xsd">
+<project xmlns="https://maven.apache.org/POM/4.0.0"
+    xmlns:xsi="https://www.w3.org/2001/XMLSchema-instance"
+    xsi:schemaLocation="https://maven.apache.org/POM/4.0.0 https://maven.apache.org/maven-v4.0.0.xsd">
     <modelVersion>4.0.0</modelVersion>
     <groupId>com.loomcom.symon</groupId>
     <artifactId>symon</artifactId>
     <packaging>jar</packaging>
-    <version>0.9.0.1</version>
+    <version>1.5.1k</version>
     <name>symon</name>
-    <url>http://www.loomcom.com/symon</url>
+    <url>https://git.loomcom.com/seth/symon</url>
     <properties>
         <project.build.sourceEncoding>
             UTF-8
@@ -17,86 +18,80 @@
     </properties>
     <repositories>
         <repository>
-            <id>jline</id>
-            <name>JLine Project Repository</name>
-            <url>http://jline.sourceforge.net/m2repo</url>
-        </repository>
-        <!-- Loomcom's Maven2 repository for JTerminal -->
-        <repository>
-            <releases>
-                <enabled>true</enabled>
-                <updatePolicy>always</updatePolicy>
-                <checksumPolicy>fail</checksumPolicy>
-            </releases>
-            <id>com.loomcom</id>
-            <name>Loom Communications Maven2 Repository</name>
-            <url>http://www.loomcom.com/maven2</url>
-            <layout>default</layout>
+            <id>jitpack.io</id>
+            <url>https://jitpack.io</url>
         </repository>
     </repositories>
     <dependencies>
         <dependency>
-            <groupId>junit</groupId>
-            <artifactId>junit</artifactId>
-            <version>4.11</version>
-            <scope>test</scope>
+            <groupId>ch.qos.logback</groupId>
+            <artifactId>logback-classic</artifactId>
+            <version>1.5.34</version>
         </dependency>
         <dependency>
-            <groupId>com.grahamedgecombe.jterminal</groupId>
-            <artifactId>jterminal</artifactId>
-            <version>1.0.2.3-loomcom</version>
+            <groupId>commons-cli</groupId>
+            <artifactId>commons-cli</artifactId>
+            <version>1.5.0</version>
+        </dependency>
+        <dependency>
+            <groupId>com.formdev</groupId>
+            <artifactId>flatlaf</artifactId>
+            <version>3.7.1</version>
+        </dependency>
+        <dependency>
+            <groupId>com.github.Dansoftowner</groupId>
+            <artifactId>jSystemThemeDetector</artifactId>
+            <version>3.9.1</version>
+        </dependency>
+        <dependency>
+            <groupId>junit</groupId>
+            <artifactId>junit</artifactId>
+            <version>4.13.2</version>
+            <scope>test</scope>
         </dependency>
         <dependency>
             <groupId>org.mockito</groupId>
-            <artifactId>mockito-all</artifactId>
-            <version>1.9.5</version>
+            <artifactId>mockito-core</artifactId>
+            <version>4.11.0</version>
             <scope>test</scope>
         </dependency>
+        <dependency>
+            <groupId>net.java.dev.jna</groupId>
+            <artifactId>jna</artifactId>
+            <version>5.14.0</version>
+        </dependency>
     </dependencies>
 
     <build>
         <plugins>
-            <plugin>
-                <artifactId>maven-resources-plugin</artifactId>
-                <version>2.6</version>
-                <executions>
-                    <execution>
-                        <id>copy-resources</id>
-                        <phase>process-resources</phase>
-                        <goals>
-                            <goal>copy-resources</goal>
-                        </goals>
-                        <configuration>
-                            <outputDirectory>${basedir}/target/classes/com/loomcom/symon/ui/images</outputDirectory>
-                            <resources>
-                                <resource>
-                                    <directory>src/main/java/com/loomcom/symon/ui/images</directory>
-                                </resource>
-                            </resources>
-                        </configuration>
-                    </execution>
-                </executions>
-            </plugin>
             <plugin>
                 <groupId>org.apache.maven.plugins</groupId>
-                <artifactId>maven-assembly-plugin</artifactId>
-                <version>2.4</version>
+                <artifactId>maven-shade-plugin</artifactId>
+                <version>3.2.0</version>
                 <configuration>
-                    <descriptorRefs>
-                        <descriptorRef>jar-with-dependencies</descriptorRef>
-                    </descriptorRefs>
-                    <appendAssemblyId>false</appendAssemblyId>
-                    <archive>
-                        <manifest>
-                            <mainClass>com.loomcom.symon.Simulator</mainClass>
-                        </manifest>
-                    </archive>
+                    <transformers>
+                        <transformer
+                                implementation="org.apache.maven.plugins.shade.resource.ManifestResourceTransformer">
+                            <mainClass>com.loomcom.symon.Main</mainClass>
+                        </transformer>
+                    </transformers>
+                    <filters>
+                        <filter>
+                            <artifact>*:*</artifact>
+                            <excludes>
+                                <exclude>META-INF/*.SF</exclude>
+                                <exclude>META-INF/*.DSA</exclude>
+                                <exclude>META-INF/*.RSA</exclude>
+                            </excludes>
+                        </filter>
+                    </filters>
                 </configuration>
                 <executions>
                     <execution>
+                        <id>make-assembly</id>
                         <phase>package</phase>
                         <goals>
-                            <goal>single</goal>
+                            <goal>shade</goal>
                         </goals>
                     </execution>
                 </executions>
@@ -104,11 +99,11 @@
             <plugin>
                 <groupId>org.apache.maven.plugins</groupId>
                 <artifactId>maven-compiler-plugin</artifactId>
-                <version>3.1</version>
+                <version>3.7.0</version>
                 <configuration>
                     <compilerArgument>-Xlint:unchecked</compilerArgument>
-                    <source>1.6</source>
-                    <target>1.6</target>
+                    <source>16</source>
+                    <target>16</target>
                 </configuration>
             </plugin>
 
@@ -116,7 +111,7 @@
             <plugin>
                 <groupId>org.apache.maven.plugins</groupId>
                 <artifactId>maven-jar-plugin</artifactId>
-                <version>2.4</version>
+                <version>3.2.0</version>
                 <configuration>
                     <archive>
                         <manifest>
@@ -148,4 +143,4 @@
             </plugin>
         </plugins>
     </build>
-</project>
+</project>

samples/README

@@ -6,32 +6,37 @@ Sample Programs
   When loaded at address $0300, this program will print "Hello, 6502 World!" in
   infinite loop.
 
-2. echo.prg
+2. echo_poll.prg
 
   When loaded at address $0300, this program will echo back to the console
   anything typed.
 
-
-Both hello.prg and echo.prg were assembled with the Ophis assembler:
+Both hello.prg and echo_poll.prg were assembled with the Ophis assembler:
 
    https://hkn.eecs.berkeley.edu/~mcmartin/ophis/
 
+3. echo_irq.rom
 
-3. ehbasic.rom
+  This is another echo program, and behaves identically to echo_poll.prg,
+  except it is interrupt-driven. This ROM can be loaded either through the
+  "File->Load ROM..." menu in Symon, or by specifying the path to
+  "echo_irq.rom" with the "-jar" command line option when running Symon,
+  for example: `java -jar symon-1.3.2.jar -rom samples/echo_irq.rom`
+
+4. ehbasic.rom
 
    This is Lee Davison's Enhanced 6502 BASIC.
 
-   To use this ROM image, just copy the file 'ehbasic.rom' into the directory
-   where you run Symon. Rename the file to 'rom.bin'.  When you start Symon,
-   the ROM file will be automatically loaded at address $d000.
+   The EhBASIC ROM can be loaded either through the "File -> Load ROM..."
+   menu in Symon, or by specifying the path to "ehbasic.rom" with
+   the "-jar" command line option when running Symon, for example:
+   `java -jar symon-1.3.2.jar -rom samples/ehbasic.rom`
 
    Click the "Run" button and EhBASIC should automatically start running.
 
    Type 'C' to do a cold start.
 
-   Then, type $C000 when prompted for the memory size.
-
-   NOTE: EhBASIC only wants upper-case input. This confused me at first!
+   Then, type '49152' (without the quotes) when prompted for the memory size.
 
    More information can be found in the 'ehbasic' directory, and by visiting
    the EhBASIC web page:

samples/echo_irq/.gitignore

@@ -0,0 +1,4 @@
+*.rom
+*.lst
+*.map
+*.o

samples/echo_irq/Makefile

@@ -0,0 +1,13 @@
+CA=ca65
+LD=ld65
+
+all: echo_irq
+
+echo_irq: echo_irq.o
+	$(LD) -C symon.config -vm -m echo_irq.map -o echo_irq.rom echo_irq.o
+
+echo_irq.o:
+	$(CA) --listing echo_irq.lst -o echo_irq.o echo_irq.asm
+
+clean:
+	rm -f *.o *.rom *.map *.lst

samples/echo_irq/echo_irq.asm

@@ -0,0 +1,48 @@
+;;
+;; Read input from the keyboard, and echo to console.
+;;
+
+
+IOBASE   = $8800
+IOSTATUS = IOBASE + 1
+IOCMD    = IOBASE + 2
+IOCTRL   = IOBASE + 3
+
+.segment "CODE"
+.org $C000
+
+START:  CLI
+        LDA #$09
+        STA IOCMD      ; Set command status
+        LDA #$1A
+        STA IOCTRL     ; 0 stop bits, 8 bit word, 2400 baud
+
+;;
+;; Infinite idle loop, waiting for interrupt.
+;;
+IDLE:   LDA #$FF
+        TAX
+IDLE1:  DEX
+        BNE IDLE1
+        JMP IDLE
+
+;;
+;; IRQ handler
+;;
+IRQ:    LDA IOBASE      ; Get the character in the ACIA.
+        PHA             ; Save accumulator
+ECHO1:  LDA IOSTATUS    ; Read the ACIA status
+        AND #$10        ; Is the tx register empty?
+        BEQ ECHO1       ; No, wait for it to empty
+        PLA             ; Otherwise, load saved accumulator,
+        STA IOBASE      ; write to output,
+        RTI             ; and return
+
+; system vectors
+
+.segment "VECTORS"
+.org    $FFFA
+
+.word   IRQ         ; NMI vector
+.word   START       ; RESET vector
+.word   IRQ         ; IRQ vector

samples/echo_irq/symon.config

@@ -0,0 +1,16 @@
+MEMORY {
+RAM1: start = $0000, size = $8000 - __STACKSIZE__;
+ROM1: start = $C000, size = $3FFA, fill = yes;
+ROMV: start = $FFFA, size = $6, file = %O, fill = yes;
+}
+
+SEGMENTS {
+CODE:     load = ROM1, type = ro;
+DATA:     load = ROM1, type = ro;
+VECTORS:  load = ROMV, type = ro;
+}
+
+SYMBOLS {
+__STACKSIZE__: type = weak, value = $0300;
+}
+

samples/ehbasic/Makefile

@@ -7,7 +7,7 @@ ehbasic: ehbasic.o
 	$(LD) -C symon.config -vm -m ehbasic.map -o ehbasic.rom ehbasic.o
 
 ehbasic.o:
-	$(CA) --listing -o ehbasic.o min_mon.asm
+	$(CA) --listing ehbasic.lst -o ehbasic.o min_mon.asm
 
 clean:
 	rm -f *.o *.rom *.map *.lst

samples/ehbasic/min_mon.asm

@@ -150,7 +150,7 @@ END_CODE
 ; sign on string
 
 LAB_mess
-	.byte	$0D,$0A,"Symon (c) 2008-2013, Seth Morabito"
+	.byte	$0D,$0A,"Symon (c) 2008-2014, Seth Morabito"
 	.byte   $0D,$0A,"Enhanced 6502 BASIC 2.22 (c) Lee Davison"
 	.byte   $0D,$0A,"[C]old/[W]arm ?",$00
 

samples/ehbasic/symon.config

@@ -1,5 +1,5 @@
 MEMORY {
-RAM1: start = $0000, size = $8000;
+RAM1: start = $0000, size = $8000 - __STACKSIZE__;
 ROM1: start = $C000, size = $3F00, fill = yes;
 MONITOR: start = $FF00, size = $FA, fill = yes;
 ROMV: start = $FFFA, size = $6, file = %O, fill = yes;
@@ -13,6 +13,6 @@ VECTORS:  load = ROMV, type = ro;
 }
 
 SYMBOLS {
-__STACKSIZE__ = $0300;
+__STACKSIZE__: type = weak, value = $0300;
 }
 

samples/ehbasic_crtc/.gitignore

@@ -0,0 +1,4 @@
+*.rom
+*.lst
+*.map
+*.o

samples/ehbasic_crtc/Makefile

@@ -0,0 +1,13 @@
+CA=ca65
+LD=ld65
+
+all: ehbasic
+
+ehbasic: ehbasic.o
+	$(LD) -C symon.config -vm -m ehbasic.map -o ehbasic.rom ehbasic.o
+
+ehbasic.o:
+	$(CA) --listing ehbasic.lst -o ehbasic.o min_mon.asm
+
+clean:
+	rm -f *.o *.rom *.map *.lst

samples/ehbasic_crtc/README.txt

@@ -0,0 +1,85 @@
+This directoy contains a very slightly modified version of EhBASIC 2.22
+to support the Symon simulator.
+
+Usage
+-----
+
+The pre-assemled ROM image 'ehbasic.rom' in the "samples" directory is all you
+need unless you want to rebuild this source code.
+
+Just copy the image 'ehbasic.rom' to the directory where you run Symon, and
+rename the file to 'rom.bin'. It will be loaded at memory location $D000 when
+the simulator starts up. Click "Run" and you'll be presented with BASIC.
+
+At the first prompt, type 'C' for a Cold Start
+
+When prompted for free memory, type: $C000
+
+Note that EhBASIC only accepts upper case input, so you'll need to use caps
+lock (the cruise control for cool) to really make the most of it.
+
+
+Building
+--------
+
+
+To build it, you'll need the CC65 tool chain from http://www.cc65.org/
+and a suitable version of 'make'. Just typing:
+
+   % make
+   
+in this directory should re-build everything. You'll get a listing,
+some object files, and the ROM image itself.
+
+
+Changes from the EhBASIC 2.22
+-----------------------------
+
+  - Minor syntax changes to allow assembly with the cc65 tool chain.
+
+  - Memory map modified for Symon.
+
+  - At reset, configure the 6551 ACIA for 8-N-1, 2400 baud.
+ 
+  - Monitor routines 'ACIAin' and 'ACIAout' modified for the 6551 ACIA.
+    Specifically, reading and writing will check the 6551 status register for
+    the status of rx and tx registers before receive or transmit.
+
+EhBASIC is copyright Lee Davison <leeedavison@googlemail.com>
+
+My changes are so slight that I hesitate to even say this, but for "CYA"
+reasons:
+
+Changes are copyright Seth Morabito <web@loomcom.com> and are distributed under
+the same license as EhBASIC. I claim no commercial interest whatsoever. Any
+commercial use must be negotiated directly with Lee Davison.
+
+
+Original EhBASIC 2.22 README
+----------------------------
+
+ Enhanced BASIC is a BASIC interpreter for the 6502 family microprocessors. It
+ is constructed to be quick and powerful and easily ported between 6502 systems.
+ It requires few resources to run and includes instructions to facilitate easy
+ low level handling of hardware devices. It also retains most of the powerful
+ high level instructions from similar BASICs.
+
+ EhBASIC is free but not copyright free. For non commercial use there is only one
+ restriction, any derivative work should include, in any binary image distributed,
+ the string "Derived from EhBASIC" and in any distribution that includes human
+ readable files a file that includes the above string in a human readable form
+ e.g. not as a comment in an HTML file.
+
+ For commercial use please contact me,  Lee Davison, at leeedavison@googlemail.com
+ for conditions.
+
+ For more information on EhBASIC, other versions of EhBASIC and other projects
+ please visit my site at ..
+
+	 http://mycorner.no-ip.org/index.html
+
+
+ P.S. c't magazin, henceforth refered to as "those thieving german bastards", are
+ prohibited from using this or any version of EhBASIC for any of their projects
+ or products. The excuse "we don't charge people for it" doesn't wash, it adds
+ value to your product so you owe me.

samples/ehbasic_crtc/min_mon.asm

@@ -0,0 +1,449 @@
+
+; minimal monitor for EhBASIC and 6502 simulator V1.05
+
+; To run EhBASIC on the simulator load and assemble [F7] this file, start the simulator
+; running [F6] then start the code with the RESET [CTRL][SHIFT]R. Just selecting RUN
+; will do nothing, you'll still have to do a reset to run the code.
+
+	.feature labels_without_colons
+	.include "basic.asm"
+
+; put the IRQ and MNI code in RAM so that it can be changed
+
+IRQ_vec	= VEC_SV+2		; IRQ code vector
+NMI_vec	= IRQ_vec+$0A	; NMI code vector
+
+; setup for the 6502 simulator environment
+
+IO_AREA		= $8800
+ACIAdata	= IO_AREA	; simulated ACIA r/w port
+ACIAstatus	= IO_AREA+1
+ACIAcommand	= IO_AREA+2
+ACIAcontrol	= IO_AREA+3
+
+	CRTC_A	= $9000		; CRTC register select
+	CRTC_C	= $9001		; CRTC register IO
+	CADDR_L	= $E0		; Cursor address (low)
+	CADDR_H	= $E1		; Cursor address (high)
+	C_COL	= $E2		; Cursor column
+	C_ROW	= $E3		; Cursor row
+	COUTC	= $E4		; Temp storage for char out.
+	R_STRT	= $E5		; E5,E6 contains starting address of
+				; current row
+	R_NXT	= $E7		; E7,E8 contains starting address of
+				; next row
+
+	N_ROWS	= 24
+	N_COLS	= 40
+
+
+; now the code. all this does is set up the vectors and interrupt code
+; and wait for the user to select [C]old or [W]arm start. nothing else
+; fits in less than 128 bytes
+
+.segment "MONITOR"
+	.org	$FC00		; pretend this is in a 1/8K ROM
+
+; reset vector points here
+
+RES_vec:
+	CLD			; clear decimal mode
+	LDX	#$FF		; empty stack
+	TXS			; set the stack
+
+	;; Initialize the CRTC
+	LDA	#$01
+	STA	CRTC_A
+	LDA	#N_COLS		; 40 columns
+	STA	CRTC_C
+	LDA	#$06
+	STA	CRTC_A
+	LDA	#N_ROWS		; 24 rows
+	STA	CRTC_C
+	LDA	#$70
+	STA	CADDR_H
+	LDA	#$00
+	STA	CADDR_L
+	STA	C_ROW
+	STA	C_COL
+	JSR	CLRVID
+	;; TODO: Initialize params on CRTC
+
+; Initialize the ACIA
+ACIA_init:
+	LDA	#$00
+	STA	ACIAstatus		; Soft reset
+	LDA	#$0B
+	STA	ACIAcommand		; Parity disabled, IRQ disabled
+	LDA	#$1E
+	STA	ACIAcontrol		; Set output for 8-N-1 9600
+
+; set up vectors and interrupt code, copy them to page 2
+
+	LDY	#END_CODE-LAB_vec	; set index/count
+LAB_stlp:
+	LDA	LAB_vec-1,Y		; get byte from interrupt code
+	STA	VEC_IN-1,Y		; save to RAM
+	DEY				; decrement index/count
+	BNE	LAB_stlp		; loop if more to do
+
+; now do the signon message, Y = $00 here
+
+LAB_signon:
+	LDA	LAB_mess,Y	; get byte from sign on message
+	BEQ	LAB_nokey	; exit loop if done
+
+	JSR	V_OUTP		; output character
+	INY			; increment index
+	BNE	LAB_signon	; loop, branch always
+
+LAB_nokey:
+	JSR	V_INPT		; call scan input device
+	BCC	LAB_nokey	; loop if no key
+
+	AND	#$DF		; mask xx0x xxxx, ensure upper case
+	CMP	#'W'		; compare with [W]arm start
+	BEQ	LAB_dowarm	; branch if [W]arm start
+
+	CMP	#'C'		; compare with [C]old start
+	BNE	RES_vec		; loop if not [C]old start
+
+	JMP	LAB_COLD	; do EhBASIC cold start
+
+LAB_dowarm:
+	JMP	LAB_WARM	; do EhBASIC warm start
+
+
+ACIAout:
+
+	PHA
+@loop:	LDA	ACIAstatus
+	AND	#$10
+	BEQ	@loop		; Wait for buffer to empty
+	PLA
+	STA	ACIAdata
+	RTS
+
+;;; Byte out to the CRTC
+;;;
+;;; 1. Increment cursor position.
+;;; 2. Scroll if necessary.
+;;; 3. Store new cursor position in CRTC.
+
+CRTCout:
+	JSR	ACIAout		; Also echo to terminal for debugging.
+
+	;; In parallel, we're maintaining two states:
+	;;    - The address of the cursor, and
+	;;    - The Column/Row of the cursor.
+	;;
+	;; The latter state is used to handle scrolling and
+	;; for knowing how far to back up the cursor
+	;; for a carriage-return.
+
+	;; Backspace
+	CMP	#$08
+	BEQ	DO_BS
+	;; Line Feed
+	CMP	#$0a
+	BEQ	DO_LF
+	;; Carriage Return
+	CMP	#$0d
+	BEQ	DO_CR
+	;; Any other character...
+	STA	COUTC		; Store the character going out
+	JSR	COUT1		; Output it where the cursor is.
+	;; We might need to scroll...
+	LDA	C_ROW
+	CMP	#N_ROWS-1
+	BNE	@noscr
+	LDA	C_COL
+	CMP	#N_COLS-1
+	BNE	@noscr
+	;; ... yup, we DO need to scroll.
+	JSR	DO_SCROLL
+	RTS
+@noscr:	JSR	INC_CADDR
+	INC	C_COL
+	JSR	SET_CURSOR
+	RTS
+
+	;; Handle a back-space character.
+DO_BS:	LDA	C_COL
+	BNE	@l1		; Skip next bit
+	LDA	#N_COLS-1
+	STA	C_COL
+	BNE	@l2
+@l1:	DEC	C_COL
+@l2:	JSR	DEC_CADDR	; Back up
+	JSR	SET_CURSOR
+
+@l3:	LDA	#$20
+	STA	COUTC		; Echo a space ($20)
+	JSR	COUT1
+	RTS
+
+DO_LF:	RTS			; Just swallow LF. CR emulates it.
+
+DO_CR:	SEC
+	LDA	CADDR_L		; 1. Carriage return to start of row.
+	SBC	C_COL
+	STA	CADDR_L
+	LDA	CADDR_H
+	SBC	#$00		; Will decrement H if carry was left
+				; set.
+	STA	CADDR_H
+
+	;; 1. Are we on the last row? Scroll.
+	LDA	C_ROW
+	CMP	#N_ROWS-1
+	BNE	@inc
+	JSR	DO_SCROLL
+	RTS
+
+@inc:	JSR	INCROW
+
+@lf:	CLC
+	LDA	CADDR_L
+	ADC	#$28		; Now add $28
+	STA	CADDR_L
+	LDA	CADDR_H
+	ADC	#$00		; Will increment if carry was set
+	STA	CADDR_H
+
+	LDA	#$00		; Reset cursor row to 0
+	STA	C_COL
+	JSR	SET_CURSOR
+	RTS
+
+SET_CURSOR:
+	LDA	#14
+	STA	CRTC_A
+	LDA	CADDR_H
+	STA	CRTC_C
+	LDA	#15
+	STA	CRTC_A
+	LDA	CADDR_L
+	STA	CRTC_C
+	RTS
+
+	;; Increment C_ROW and put new
+	;; line start address in R_STRT,R_STRT+1
+INCROW:	TYA
+	PHA
+	INC	C_ROW
+	BNE	DECR2	      ; Share code with DECROW
+
+	;; Decrement C_ROW and put new
+	;; line start address in R_STRT,R_STRT+1
+DECROW:	TYA
+	PHA
+	DEC	C_ROW
+DECR2:	JSR	SETRSTRT
+	PLA
+	TAY
+	RTS
+
+	;; Send the cursor home to the start of the line
+HOME:
+	LDY	C_ROW
+	LDA	CRA_LO,Y
+	STA	CADDR_L
+	LDA	CRA_HI,Y
+	STA	CADDR_H
+	LDA	#$00
+	STA	C_COL
+	RTS
+
+	;; Set the start address of the current row
+SETRSTRT:
+	LDY	C_ROW
+	LDA	CRA_LO,Y
+	STA	R_STRT
+	LDA	CRA_HI,Y
+	STA	R_STRT+1
+	RTS
+
+	;; Clear the current video line
+CLRLN:	LDA	#$20
+	LDY	#$00
+@l1:	STA	(R_STRT),Y
+	INY
+	CPY	#N_COLS
+	BNE	@l1
+	RTS
+
+	;; Clear the video window and put the cursor at the home
+	;; position
+CLRVID:
+	LDA	#$20
+	LDX	#N_ROWS-1
+@l1:	STX	C_ROW
+	JSR	SETRSTRT
+	JSR	CLRLN
+	DEX
+	BPL	@l1
+	RTS
+
+	;; Handle a scroll request.
+	;;
+	;; The cursor could be anywhere on the line when this scroll
+	;; request comes in.
+DO_SCROLL:
+	PHA
+	TYA
+	PHA
+	TXA
+	PHA
+
+	;; The idea here is to copy each line to the line above it
+	LDX	#$00
+
+@l1:	LDA	CRA_LO,X
+	STA	R_STRT
+	LDA	CRA_HI,X
+	STA	R_STRT+1
+
+	INX
+
+	LDA	CRA_LO,X
+	STA	R_NXT
+	LDA	CRA_HI,X
+	STA	R_NXT+1
+
+	LDY	#0
+@l2:	LDA	(R_NXT),Y
+	STA	(R_STRT),Y
+	INY
+	CPY	#N_COLS
+	BNE	@l2
+
+	CPX	#N_ROWS
+	BNE	@l1
+
+	;; Clear the line the cursor occupies.
+	JSR	CLRLN
+
+	;; Move the cursor to the beginning of the line
+	JSR	HOME
+	JSR	SET_CURSOR
+
+	PLA
+	TAX
+	PLA
+	TAY			; Restore Y
+	PLA
+	RTS
+
+	;; Decrement the cursor address
+INC_CADDR:
+	INC	CADDR_L
+	BNE	@l1		; Did we increment to 0?
+	INC	CADDR_H		; Yes, also increment high
+@l1:	RTS
+
+	;; Increment the cursor address
+DEC_CADDR:
+	CMP	CADDR_L		; Is low alrady 0?
+	BNE	@l1
+	DEC	CADDR_H		; Yes, decrement high
+@l1:	DEC	CADDR_L
+	RTS
+
+COUT1:
+	TYA
+	PHA			; Save Y
+	LDY	#$00
+	LDA	COUTC
+	STA	(CADDR_L),Y
+	PLA
+	TAY			; Restore Y
+	RTS
+
+;;;
+;;; byte in from ACIA. This subroutine will also force
+;;; all lowercase letters to be uppercase, because EhBASIC
+;;; only understands upper-case tokens
+;;;
+ACIAin:
+	LDA	ACIAstatus	; Read 6551 status
+	AND	#$08		;
+	BEQ	LAB_nobyw	; If rx buffer empty, no byte
+
+	LDA	ACIAdata	; Read byte from 6551
+	CMP	#'a'		; Is it < 'a'?
+	BCC	@done		; Yes, we're done
+	CMP	#'{'		; Is it >= '{'?
+	BCS	@done		; Yes, we're done
+	AND	#$5f		; Otherwise, mask to uppercase
+@done:
+	SEC			; Flag byte received
+	RTS
+
+LAB_nobyw:
+	CLC			; flag no byte received
+no_load:			; empty load vector for EhBASIC
+no_save:			; empty save vector for EhBASIC
+	RTS
+
+; vector tables
+
+LAB_vec:
+	.word	ACIAin		; byte in from simulated ACIA
+	.word	CRTCout		; byte out to simulated ACIA
+	.word	no_load		; null load vector for EhBASIC
+	.word	no_save		; null save vector for EhBASIC
+
+; EhBASIC IRQ support
+
+IRQ_CODE:
+	PHA			; save A
+	LDA	IrqBase		; get the IRQ flag byte
+	LSR			; shift the set b7 to b6, and on down ...
+	ORA	IrqBase		; OR the original back in
+	STA	IrqBase		; save the new IRQ flag byte
+	PLA			; restore A
+	RTI
+
+; EhBASIC NMI support
+
+NMI_CODE:
+	PHA			; save A
+	LDA	NmiBase		; get the NMI flag byte
+	LSR			; shift the set b7 to b6, and on down ...
+	ORA	NmiBase		; OR the original back in
+	STA	NmiBase		; save the new NMI flag byte
+	PLA			; restore A
+	RTI
+
+END_CODE:
+
+
+;;; CRTC row addresses: HIGH
+CRA_HI:
+	.byte	$70,$70,$70,$70,$70,$70,$70,$71
+	.byte	$71,$71,$71,$71,$71,$72,$72,$72
+	.byte	$72,$72,$72,$72,$73,$73,$73,$73
+
+
+;;; CRTC row addresses: LOW
+CRA_LO:
+	.byte	$00,$28,$50,$78,$A0,$C8,$F0,$18
+	.byte	$40,$68,$90,$B8,$E0,$08,$30,$58
+	.byte	$80,$A8,$D0,$F8,$20,$48,$70,$98
+
+; sign on string
+LAB_mess:
+	.byte	$0D,$0A,"SYMON (C) 2008-2014, SETH MORABITO"
+	.byte   $0D,$0A,"ENHANCED 6502 BASIC 2.22 (C) LEE DAVISON"
+	.byte   $0D,$0A,"[C]OLD/[W]ARM ?",$00
+
+
+; system vectors
+
+.segment "VECTORS"
+	.org	$FFFA
+
+	.word	NMI_vec		; NMI vector
+	.word	RES_vec		; RESET vector
+	.word	IRQ_vec		; IRQ vector

samples/ehbasic_crtc/symon.config

@@ -0,0 +1,18 @@
+MEMORY {
+RAM1: start = $0000, size = $8000 - __STACKSIZE__;
+ROM1: start = $C000, size = $3C00, fill = yes;
+MONITOR: start = $FC00, size = $3FA, fill = yes;
+ROMV: start = $FFFA, size = $6, file = %O, fill = yes;
+}
+
+SEGMENTS {
+CODE:     load = ROM1, type = ro;
+DATA:     load = ROM1, type = ro;
+MONITOR:  load = MONITOR, type = ro;
+VECTORS:  load = ROMV, type = ro;
+}
+
+SYMBOLS {
+__STACKSIZE__: type = weak, value = $0300;
+}
+

src/main/java/com/loomcom/symon/Breakpoints.java

@@ -0,0 +1,103 @@
+/*
+ * Copyright (c) 2008-2025 Seth J. Morabito <web@loomcom.com>
+ *
+ * Permission is hereby granted, free of charge, to any person obtaining
+ * a copy of this software and associated documentation files (the
+ * "Software"), to deal in the Software without restriction, including
+ * without limitation the rights to use, copy, modify, merge, publish,
+ * distribute, sublicense, and/or sell copies of the Software, and to
+ * permit persons to whom the Software is furnished to do so, subject to
+ * the following conditions:
+ *
+ * The above copyright notice and this permission notice shall be
+ * included in all copies or substantial portions of the Software.
+ *
+ * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND,
+ * EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF
+ * MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND
+ * NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS BE
+ * LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION
+ * OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION
+ * WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.
+ */
+
+package com.loomcom.symon;
+
+import com.loomcom.symon.exceptions.MemoryAccessException;
+import com.loomcom.symon.util.Utils;
+
+import javax.swing.table.AbstractTableModel;
+import java.util.ArrayList;
+import java.util.TreeSet;
+
+public class Breakpoints extends AbstractTableModel {
+
+    private final TreeSet<Integer> breakpoints;
+    private final Simulator simulator;
+
+    public Breakpoints(Simulator simulator) {
+        this.breakpoints = new TreeSet<>();
+        this.simulator = simulator;
+    }
+
+    public boolean contains(int address) {
+        return this.breakpoints.contains(address);
+    }
+
+    public void addBreakpoint(int address) {
+        this.breakpoints .add(address);
+        fireTableDataChanged();
+    }
+
+    public void removeBreakpointAtIndex(int index) {
+        if (index < 0) {
+            return;
+        }
+
+        ArrayList<Integer> values = new ArrayList<>(breakpoints);
+        int value = values.get(index);
+        this.breakpoints.remove(value);
+        fireTableDataChanged();
+    }
+
+    public void refresh() {
+        fireTableDataChanged();
+    }
+
+    @Override
+    public String getColumnName(int index) {
+        if (index == 0) {
+            return "Address";
+        } else {
+            return "Inst";
+        }
+    }
+
+    @Override
+    public int getRowCount() {
+        return breakpoints.size();
+    }
+
+    @Override
+    public int getColumnCount() {
+        return 2;
+    }
+
+    @Override
+    public Object getValueAt(int rowIndex, int columnIndex) {
+        ArrayList<Integer> values = new ArrayList<>(breakpoints);
+
+        if (columnIndex == 0) {
+            return "$" + Utils.wordToHex(values.get(rowIndex));
+        } else if (columnIndex == 1) {
+            int address = values.get(rowIndex);
+            try {
+                return simulator.disassembleOpAtAddress(address);
+            } catch (MemoryAccessException ex) {
+                return "???";
+            }
+        } else {
+            return null;
+        }
+    }
+}

src/main/java/com/loomcom/symon/Bus.java

@@ -1,5 +1,5 @@
 /*
- * Copyright (c) 2008-2013 Seth J. Morabito <sethm@loomcom.com>
+ * Copyright (c) 2008-2025 Seth J. Morabito <web@loomcom.com>
  *
  * Permission is hereby granted, free of charge, to any person obtaining
  * a copy of this software and associated documentation files (the
@@ -27,6 +27,12 @@ import com.loomcom.symon.devices.Device;
 import com.loomcom.symon.exceptions.MemoryAccessException;
 import com.loomcom.symon.exceptions.MemoryRangeException;
 
+import java.util.ArrayList;
+import java.util.Collections;
+import java.util.List;
+import java.util.HashMap;
+import java.util.Map;
+
 import java.util.SortedSet;
 import java.util.TreeSet;
 
@@ -36,24 +42,28 @@ import java.util.TreeSet;
 public class Bus {
 
     // The default address at which to load programs
-    public static int DEFAULT_LOAD_ADDRESS = 0x0200;
-	
+    public static final int DEFAULT_LOAD_ADDRESS = 0x0200;
+
     // By default, our bus starts at 0, and goes up to 64K
-    private int startAddress = 0x0000;
-    private int endAddress = 0xffff;
+    private final int startAddress;
+    private final int endAddress;
 
     // The CPU
     private Cpu cpu;
 
-    // Ordered list of IO devices.
-    private SortedSet<Device> devices;
+    // Ordered sets of IO devices, associated with their priority
+    private final Map<Integer, SortedSet<Device>> deviceMap;
+
+    // an array for quick lookup of addresses, brute-force style
+    private Device[] deviceAddressArray;
+
 
     public Bus(int size) {
         this(0, size - 1);
     }
 
     public Bus(int startAddress, int endAddress) {
-        this.devices = new TreeSet<Device>();
+        this.deviceMap = new HashMap<>();
         this.startAddress = startAddress;
         this.endAddress = endAddress;
     }
@@ -66,38 +76,67 @@ public class Bus {
         return endAddress;
     }
 
-    /**
-     * Add a device to the bus. Throws a MemoryRangeException if the device overlaps with any others.
-     *
-     * @param device
-     * @throws MemoryRangeException
-     */
-    public void addDevice(Device device) throws MemoryRangeException {
-        // Make sure there's no memory overlap.
-        MemoryRange memRange = device.getMemoryRange();
-        for (Device d : devices) {
-            if (d.getMemoryRange().overlaps(memRange)) {
-                throw new MemoryRangeException("The device being added at " +
-                                               String.format("$%04X", memRange.startAddress()) +
-                                               " overlaps with an existing " +
-                                               "device, '" + d + "'");
+    private void buildDeviceAddressArray() {
+        int size = (this.endAddress - this.startAddress) + 1;
+        deviceAddressArray = new Device[size];
+
+        // getDevices() provides an OrderedSet with devices ordered by priorities
+        for (Device device : getDevices()) {
+            MemoryRange range = device.getMemoryRange();
+            for (int address = range.startAddress; address <= range.endAddress; ++address) {
+                deviceAddressArray[address - this.startAddress] = device;
             }
         }
 
-        // Add the device
-        device.setBus(this);
-        devices.add(device);
     }
 
+    /**
+     * Add a device to the bus.
+     *
+     * @param device   Device to add
+     * @param priority Bus priority.
+     * @throws MemoryRangeException Invalid device address range.
+     */
+    public void addDevice(Device device, int priority) throws MemoryRangeException {
+
+        MemoryRange range = device.getMemoryRange();
+
+        if (range.startAddress() < this.startAddress || range.startAddress() > this.endAddress) {
+            throw new MemoryRangeException("start address of device " + device.getName() + " does not fall within the address range of the bus");
+        }
+
+        if (range.endAddress() < this.startAddress || range.endAddress() > this.endAddress) {
+            throw new MemoryRangeException("end address of device " + device.getName() + " does not fall within the address range of the bus");
+        }
+
+        SortedSet<Device> deviceSet = deviceMap.computeIfAbsent(priority, k -> new TreeSet<>());
+
+        device.setBus(this);
+        deviceSet.add(device);
+        buildDeviceAddressArray();
+    }
+
+    /**
+     * Add a device to the bus. Throws a MemoryRangeException if the device overlaps with any others.
+     *
+     * @param device Device to add
+     * @throws MemoryRangeException Invalid device memory range.
+     */
+    public void addDevice(Device device) throws MemoryRangeException {
+        addDevice(device, 0);
+    }
+
+
     /**
      * Remove a device from the bus.
      *
-     * @param device
+     * @param device Device to remove
      */
     public void removeDevice(Device device) {
-        if (devices.contains(device)) {
-            devices.remove(device);
+        for (SortedSet<Device> deviceSet : deviceMap.values()) {
+            deviceSet.remove(device);
         }
+        buildDeviceAddressArray();
     }
 
     public void addCpu(Cpu cpu) {
@@ -111,49 +150,79 @@ public class Bus {
      * device.
      */
     public boolean isComplete() {
-        // Empty maps cannot be complete.
-        if (devices.isEmpty()) {
-            return false;
+        if (deviceAddressArray == null) {
+            buildDeviceAddressArray();
         }
 
-        // Loop over devices and add their size
-        int filledMemory = 0;
-        for (Device d : devices) {
-            filledMemory += d.getSize();
-        }
-
-        // Returns if the total size of the devices fill the bus' memory space
-        return filledMemory == endAddress - startAddress + 1;
-    }
-
-    public int read(int address) throws MemoryAccessException {
-        for (Device d : devices) {
-            MemoryRange range = d.getMemoryRange();
-            if (range.includes(address)) {
-                // Compute offset into this device's address space.
-                int devAddr = address - range.startAddress();
-                return d.read(devAddr);
+        for (int address = startAddress; address <= endAddress; ++address) {
+            if (deviceAddressArray[address - startAddress] == null) {
+                return false;
             }
         }
+
+        return true;
+    }
+
+    public int read(int address, boolean cpuAccess) throws MemoryAccessException {
+        Device d = deviceAddressArray[address - this.startAddress];
+        if (d != null) {
+            MemoryRange range = d.getMemoryRange();
+            int devAddr = address - range.startAddress();
+            return d.read(devAddr, cpuAccess) & 0xff;
+        }
+
         throw new MemoryAccessException("Bus read failed. No device at address " + String.format("$%04X", address));
     }
 
     public void write(int address, int value) throws MemoryAccessException {
-        for (Device d : devices) {
+        Device d = deviceAddressArray[address - this.startAddress];
+        if (d != null) {
             MemoryRange range = d.getMemoryRange();
-            if (range.includes(address)) {
-                // Compute offset into this device's address space.
-                int devAddr = address - range.startAddress();
-                d.write(devAddr, value);
-                return;
-            }
+            int devAddr = address - range.startAddress();
+            d.write(devAddr, value);
+            return;
         }
+
         throw new MemoryAccessException("Bus write failed. No device at address " + String.format("$%04X", address));
     }
 
+    public void assertIrq() {
+        if (cpu != null) {
+            cpu.assertIrq();
+        }
+    }
+
+    public void clearIrq() {
+        if (cpu != null) {
+            cpu.clearIrq();
+        }
+    }
+
+    public void assertNmi() {
+        if (cpu != null) {
+            cpu.assertNmi();
+        }
+    }
+
+    public void clearNmi() {
+        if (cpu != null) {
+            cpu.clearNmi();
+        }
+    }
+
     public SortedSet<Device> getDevices() {
-        // Expose a copy of the device list, not the original
-        return new TreeSet<Device>(devices);
+        // create an ordered set of devices, ordered by device priorities
+        SortedSet<Device> devices = new TreeSet<>();
+
+        List<Integer> priorities = new ArrayList<>(deviceMap.keySet());
+        Collections.sort(priorities);
+
+        for (int priority : priorities) {
+            SortedSet<Device> deviceSet = deviceMap.get(priority);
+            devices.addAll(deviceSet);
+        }
+
+        return devices;
     }
 
     public Cpu getCpu() {

src/main/java/com/loomcom/symon/CpuState.java

@@ -0,0 +1,200 @@
+/*
+ * Copyright (c) 2008-2025 Seth J. Morabito <web@loomcom.com>
+ *
+ * Permission is hereby granted, free of charge, to any person obtaining
+ * a copy of this software and associated documentation files (the
+ * "Software"), to deal in the Software without restriction, including
+ * without limitation the rights to use, copy, modify, merge, publish,
+ * distribute, sublicense, and/or sell copies of the Software, and to
+ * permit persons to whom the Software is furnished to do so, subject to
+ * the following conditions:
+ *
+ * The above copyright notice and this permission notice shall be
+ * included in all copies or substantial portions of the Software.
+ *
+ * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND,
+ * EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF
+ * MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND
+ * NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS BE
+ * LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION
+ * OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION
+ * WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.
+ */
+
+package com.loomcom.symon;
+
+import com.loomcom.symon.util.Utils;
+
+/**
+ * A compact, struct-like representation of CPU state.
+ */
+public class CpuState {
+    /**
+     * Accumulator
+     */
+    public int a;
+
+    /**
+     * X index register
+     */
+    public int x;
+
+    /**
+     * Y index register
+     */
+    public int y;
+
+    /**
+     * Stack Pointer
+     */
+    public int sp;
+
+    /**
+     * Program Counter
+     */
+    public int pc;
+
+    /**
+     * Last Loaded Instruction Register
+     */
+    public int ir;
+
+    /**
+     * Peek-Ahead to next IR
+     */
+    public int nextIr;
+    public int[] args = new int[2];
+    public int[] nextArgs = new int[2];
+    public int instSize;
+    public boolean opTrap;
+    public boolean irqAsserted;
+    public boolean nmiAsserted;
+    public int lastPc;
+
+    /* Status Flag Register bits */
+    public boolean carryFlag;
+    public boolean negativeFlag;
+    public boolean zeroFlag;
+    public boolean irqDisableFlag;
+    public boolean decimalModeFlag;
+    public boolean breakFlag;
+    public boolean overflowFlag;
+    public long stepCounter = 0L;
+
+    public CpuState() {}
+
+    /**
+     * Snapshot a copy of the CpuState. (This is a copy constructor rather than an
+     * implementation of <code>Cloneable</code> based on Josh Bloch's recommendation)
+     *
+     * @param s The CpuState to copy.
+     */
+    @SuppressWarnings("CopyConstructorMissesField")
+    public CpuState(CpuState s) {
+        this.a = s.a;
+        this.x = s.x;
+        this.y = s.y;
+        this.sp = s.sp;
+        this.pc = s.pc;
+        this.ir = s.ir;
+        this.nextIr = s.nextIr;
+        this.lastPc = s.lastPc;
+        this.args[0] = s.args[0];
+        this.args[1] = s.args[1];
+        this.nextArgs[0] = s.nextArgs[0];
+        this.nextArgs[1] = s.nextArgs[1];
+        this.instSize = s.instSize;
+        this.opTrap = s.opTrap;
+        this.nmiAsserted = s.nmiAsserted;
+        this.irqAsserted = s.irqAsserted;
+        this.carryFlag = s.carryFlag;
+        this.negativeFlag = s.negativeFlag;
+        this.zeroFlag = s.zeroFlag;
+        this.irqDisableFlag = s.irqDisableFlag;
+        this.decimalModeFlag = s.decimalModeFlag;
+        this.breakFlag = s.breakFlag;
+        this.overflowFlag = s.overflowFlag;
+        this.stepCounter = s.stepCounter;
+    }
+
+    /**
+     * Returns a string formatted for the trace log.
+     *
+     * @return a string formatted for the trace log.
+     */
+    public String toTraceEvent() {
+        String opcode = Cpu.disassembleOp(ir, args);
+        return getInstructionByteStatus() + "  " +
+                String.format("%-14s", opcode) +
+                "A:" + Utils.byteToHex(a) + " " +
+                "X:" + Utils.byteToHex(x) + " " +
+                "Y:" + Utils.byteToHex(y) + " " +
+                "F:" + Utils.byteToHex(getStatusFlag()) + " " +
+                "S:1" + Utils.byteToHex(sp) + " " +
+                getProcessorStatusString() + "\n";
+    }
+
+    /**
+     * @return The value of the Process Status Register, as a byte.
+     */
+    public int getStatusFlag() {
+        int status = 0x20;
+        if (carryFlag) {
+            status |= Cpu.P_CARRY;
+        }
+        if (zeroFlag) {
+            status |= Cpu.P_ZERO;
+        }
+        if (irqDisableFlag) {
+            status |= Cpu.P_IRQ_DISABLE;
+        }
+        if (decimalModeFlag) {
+            status |= Cpu.P_DECIMAL;
+        }
+        if (breakFlag) {
+            status |= Cpu.P_BREAK;
+        }
+        if (overflowFlag) {
+            status |= Cpu.P_OVERFLOW;
+        }
+        if (negativeFlag) {
+            status |= Cpu.P_NEGATIVE;
+        }
+        return status;
+    }
+
+    public String getInstructionByteStatus() {
+        switch (Cpu.instructionSizes[ir]) {
+            case 0:
+            case 1:
+                return Utils.wordToHex(lastPc) + "  " +
+                       Utils.byteToHex(ir) + "      ";
+            case 2:
+                return Utils.wordToHex(lastPc) + "  " +
+                       Utils.byteToHex(ir) + " " +
+                       Utils.byteToHex(args[0]) + "   ";
+            case 3:
+                return Utils.wordToHex(lastPc) + "  " +
+                       Utils.byteToHex(ir) + " " +
+                       Utils.byteToHex(args[0]) + " " +
+                       Utils.byteToHex(args[1]);
+            default:
+                return null;
+        }
+    }
+
+    /**
+     * @return A string representing the current status register state.
+     */
+    public String getProcessorStatusString() {
+        return "[" + (negativeFlag ? 'N' : '.') +
+                (overflowFlag ? 'V' : '.') +
+                "-" +
+                (breakFlag ? 'B' : '.') +
+                (decimalModeFlag ? 'D' : '.') +
+                (irqDisableFlag ? 'I' : '.') +
+                (zeroFlag ? 'Z' : '.') +
+                (carryFlag ? 'C' : '.') +
+                "]";
+    }
+}

src/main/java/com/loomcom/symon/InstructionTable.java

@@ -1,5 +1,5 @@
 /*
- * Copyright (c) 2008-2012 Seth J. Morabito <sethm@loomcom.com>
+ * Copyright (c) 2008-2025 Seth J. Morabito <web@loomcom.com>
  *
  * Permission is hereby granted, free of charge, to any person obtaining
  * a copy of this software and associated documentation files (the
@@ -25,53 +25,54 @@ package com.loomcom.symon;
 
 public interface InstructionTable {
 
+    int BRK = 0x00;
+    int JSR = 0x20;
+    int RTS = 0x60;
+
     /**
      * Enumeration of valid CPU behaviors. These determine what behavior and instruction
      * set will be simulated, depending on desired version of 6502.
-     *
-     * TODO: As of version 0.6, this is still not used! All CPUs are "idealized" NMOS 6502 only.
      */
-    public enum CpuBehavior {
+    enum CpuBehavior {
         /**
          * The earliest NMOS 6502 includes a bug that causes the ROR instruction
          * to behave like an ASL that does not affect the carry bit. This version
          * is very rare in the wild.
-         *
-         * NB: Does NOT implement "unimplemented" NMOS instructions.
          */
         NMOS_WITH_ROR_BUG,
 
         /**
          * All NMOS 6502's have a bug with the indirect JMP instruction. If the
-         *
-         * NB: Does NOT implement "unimplemented" NMOS instructions.
          */
-        NMOS_WITH_INDIRECT_JMP_BUG,
-
-        /**
-         * Emulate an NMOS 6502 without the indirect JMP bug. This type of 6502
-         * does not actually exist in the wild.
-         *
-         * NB: Does NOT implement "unimplemented" NMOS instructions.
-         */
-        NMOS_WITHOUT_INDIRECT_JMP_BUG,
+        NMOS_6502,
 
         /**
          * Emulate a CMOS 65C02, with all CMOS instructions and addressing modes.
          */
-        CMOS
+        CMOS_6502,
+
+        /**
+         * Emulate a CMOS 65C816.
+         */
+        CMOS_65816
     }
 
     /**
      * Enumeration of Addressing Modes.
      */
-    public enum Mode {
+    enum Mode {
         ACC {
             public String toString() {
                 return "Accumulator";
             }
         },
 
+        AIX {
+            public String toString() {
+                return "Absolute, X-Indexed Indirect";
+            }
+        },
+
         ABS {
             public String toString() {
                 return "Absolute";
@@ -128,19 +129,31 @@ public interface InstructionTable {
 
         ZPG {
             public String toString() {
-                return "Zeropage";
+                return "Zero Page";
+            }
+        },
+
+        ZPR {
+            public String toString() {
+                return "Zero Page, Relative";
             }
         },
 
         ZPX {
             public String toString() {
-                return "Zeropage, X-indexed";
+                return "Zero Page, X-indexed";
             }
         },
 
         ZPY {
             public String toString() {
-                return "Zeropage, Y-indexed";
+                return "Zero Page, Y-indexed";
+            }
+        },
+
+        ZPI {
+            public String toString() {
+                return "Zero Page Indirect";
             }
         },
 
@@ -154,156 +167,188 @@ public interface InstructionTable {
     // 6502 opcodes.  No 65C02 opcodes implemented.
 
     /**
-     * Instruction opcode names.
+     * Instruction opcode names. This lists all opcodes for
+     * NMOS 6502, CMOS 65C02, and CMOS 65C816.
+     * <p>
+     * TODO (2025-03-14): This table is clearly wrong for 65C816.
+     * TODO (2025-03-14): Rockwell/WDC 65C02 names conflict with 65C816 names.
      */
-    public static final String[] opcodeNames = {
-        "BRK", "ORA",  null,  null,  null, "ORA", "ASL",  null,
-        "PHP", "ORA", "ASL",  null,  null, "ORA", "ASL",  null,
-        "BPL", "ORA",  null,  null,  null, "ORA", "ASL",  null,
-        "CLC", "ORA",  null,  null,  null, "ORA", "ASL",  null,
-        "JSR", "AND",  null,  null, "BIT", "AND", "ROL",  null,
-        "PLP", "AND", "ROL",  null, "BIT", "AND", "ROL",  null,
-        "BMI", "AND",  null,  null,  null, "AND", "ROL",  null,
-        "SEC", "AND",  null,  null,  null, "AND", "ROL",  null,
-        "RTI", "EOR",  null,  null,  null, "EOR", "LSR",  null,
-        "PHA", "EOR", "LSR",  null, "JMP", "EOR", "LSR",  null,
-        "BVC", "EOR",  null,  null,  null, "EOR", "LSR",  null,
-        "CLI", "EOR",  null,  null,  null, "EOR", "LSR",  null,
-        "RTS", "ADC",  null,  null,  null, "ADC", "ROR",  null,
-        "PLA", "ADC", "ROR",  null, "JMP", "ADC", "ROR",  null,
-        "BVS", "ADC",  null,  null,  null, "ADC", "ROR",  null,
-        "SEI", "ADC",  null,  null,  null, "ADC", "ROR",  null,
-        "BCS", "STA",  null,  null, "STY", "STA", "STX",  null,
-        "DEY",  null, "TXA",  null, "STY", "STA", "STX",  null,
-        "BCC", "STA",  null,  null, "STY", "STA", "STX",  null,
-        "TYA", "STA", "TXS",  null,  null, "STA",  null,  null,
-        "LDY", "LDA", "LDX",  null, "LDY", "LDA", "LDX",  null,
-        "TAY", "LDA", "TAX",  null, "LDY", "LDA", "LDX",  null,
-        "BCS", "LDA",  null,  null, "LDY", "LDA", "LDX",  null,
-        "CLV", "LDA", "TSX",  null, "LDY", "LDA", "LDX",  null,
-        "CPY", "CMP",  null,  null, "CPY", "CMP", "DEC",  null,
-        "INY", "CMP", "DEX",  null, "CPY", "CMP", "DEC",  null,
-        "BNE", "CMP",  null,  null,  null, "CMP", "DEC",  null,
-        "CLD", "CMP",  null,  null,  null, "CMP", "DEC",  null,
-        "CPX", "SBC",  null,  null, "CPX", "SBC", "INC",  null,
-        "INX", "SBC", "NOP",  null, "CPX", "SBC", "INC",  null,
-        "BEQ", "SBC",  null,  null,  null, "SBC", "INC",  null,
-        "SED", "SBC",  null,  null,  null, "SBC", "INC",  null
+    String[] opcodeNames = {
+        "BRK", "ORA", "NOP", "NOP", "TSB", "ORA", "ASL", "RMB0",  // 0x00-0x07
+        "PHP", "ORA", "ASL", "NOP", "TSB", "ORA", "ASL", "BBR0",  // 0x08-0x0f
+        "BPL", "ORA", "ORA", "NOP", "TRB", "ORA", "ASL", "RMB1",  // 0x10-0x17
+        "CLC", "ORA", "INC", "NOP", "TRB", "ORA", "ASL", "BBR1",  // 0x18-0x1f
+        "JSR", "AND", "NOP", "NOP", "BIT", "AND", "ROL", "RMB2",  // 0x20-0x27
+        "PLP", "AND", "ROL", "NOP", "BIT", "AND", "ROL", "BBR2",  // 0x28-0x2f
+        "BMI", "AND", "AND", "NOP", "BIT", "AND", "ROL", "RMB3",  // 0x30-0x37
+        "SEC", "AND", "DEC", "NOP", "BIT", "AND", "ROL", "BBR3",  // 0x38-0x3f
+        "RTI", "EOR", "NOP", "NOP", "NOP", "EOR", "LSR", "RMB4",  // 0x40-0x47
+        "PHA", "EOR", "LSR", "NOP", "JMP", "EOR", "LSR", "BBR4",  // 0x48-0x4f
+        "BVC", "EOR", "EOR", "NOP", "NOP", "EOR", "LSR", "RMB5",  // 0x50-0x57
+        "CLI", "EOR", "PHY", "NOP", "NOP", "EOR", "LSR", "BBR5",  // 0x58-0x5f
+        "RTS", "ADC", "NOP", "NOP", "STZ", "ADC", "ROR", "RMB6",  // 0x60-0x67
+        "PLA", "ADC", "ROR", "NOP", "JMP", "ADC", "ROR", "BBR6",  // 0x68-0x6f
+        "BVS", "ADC", "ADC", "NOP", "STZ", "ADC", "ROR", "RMB7",  // 0x70-0x77
+        "SEI", "ADC", "PLY", "NOP", "JMP", "ADC", "ROR", "BBR7",  // 0x78-0x7f
+        "BRA", "STA", "NOP", "NOP", "STY", "STA", "STX", "SMB0",  // 0x80-0x87
+        "DEY", "BIT", "TXA", "NOP", "STY", "STA", "STX", "BBS0",  // 0x88-0x8f
+        "BCC", "STA", "STA", "NOP", "STY", "STA", "STX", "SMB1",  // 0x90-0x97
+        "TYA", "STA", "TXS", "NOP", "STZ", "STA", "STZ", "BBS1",  // 0x98-0x9f
+        "LDY", "LDA", "LDX", "NOP", "LDY", "LDA", "LDX", "SMB2",  // 0xa0-0xa7
+        "TAY", "LDA", "TAX", "NOP", "LDY", "LDA", "LDX", "BBS2",  // 0xa8-0xaf
+        "BCS", "LDA", "LDA", "NOP", "LDY", "LDA", "LDX", "SMB3",  // 0xb0-0xb7
+        "CLV", "LDA", "TSX", "NOP", "LDY", "LDA", "LDX", "BBS3",  // 0xb8-0xbf
+        "CPY", "CMP", "NOP", "NOP", "CPY", "CMP", "DEC", "SMB4",  // 0xc0-0xc7
+        "INY", "CMP", "DEX", "NOP", "CPY", "CMP", "DEC", "BBS4",  // 0xc8-0xcf
+        "BNE", "CMP", "CMP", "NOP", "NOP", "CMP", "DEC", "SMB5",  // 0xd0-0xd7
+        "CLD", "CMP", "PHX", "NOP", "NOP", "CMP", "DEC", "BBS5",  // 0xd8-0xdf
+        "CPX", "SBC", "NOP", "NOP", "CPX", "SBC", "INC", "SMB6",  // 0xe0-0xe7
+        "INX", "SBC", "NOP", "NOP", "CPX", "SBC", "INC", "BBS6",  // 0xe8-0xef
+        "BEQ", "SBC", "SBC", "NOP", "NOP", "SBC", "INC", "SMB7",  // 0xf0-0xf7
+        "SED", "SBC", "PLX", "NOP", "NOP", "SBC", "INC", "BBS7"   // 0xf8-0xff
     };
 
     /**
-     * Instruction addressing modes.
+     * Instruction addressing modes. This table includes sizes
+     * for all instructions for NMOS 6502, CMOS 65C02,
+     * and CMOS 65C816
      */
-    public static final Mode[] instructionModes = {
+    Mode[] instructionModes = {
         Mode.IMP, Mode.XIN, Mode.NUL, Mode.NUL,   // 0x00-0x03
-        Mode.NUL, Mode.ZPG, Mode.ZPG, Mode.NUL,   // 0x04-0x07
+        Mode.ZPG, Mode.ZPG, Mode.ZPG, Mode.ZPG,   // 0x04-0x07
         Mode.IMP, Mode.IMM, Mode.ACC, Mode.NUL,   // 0x08-0x0b
-        Mode.NUL, Mode.ABS, Mode.ABS, Mode.NUL,   // 0x0c-0x0f
-        Mode.REL, Mode.INY, Mode.NUL, Mode.NUL,   // 0x10-0x13
-        Mode.NUL, Mode.ZPX, Mode.ZPX, Mode.NUL,   // 0x14-0x17
-        Mode.IMP, Mode.ABY, Mode.NUL, Mode.NUL,   // 0x18-0x1b
-        Mode.NUL, Mode.ABX, Mode.ABX, Mode.NUL,   // 0x1c-0x1f
+        Mode.ABS, Mode.ABS, Mode.ABS, Mode.ZPR,   // 0x0c-0x0f
+        Mode.REL, Mode.INY, Mode.ZPI, Mode.NUL,   // 0x10-0x13
+        Mode.ZPG, Mode.ZPX, Mode.ZPX, Mode.ZPG,   // 0x14-0x17
+        Mode.IMP, Mode.ABY, Mode.IMP, Mode.NUL,   // 0x18-0x1b
+        Mode.ABS, Mode.ABX, Mode.ABX, Mode.ZPR,   // 0x1c-0x1f
         Mode.ABS, Mode.XIN, Mode.NUL, Mode.NUL,   // 0x20-0x23
-        Mode.ZPG, Mode.ZPG, Mode.ZPG, Mode.NUL,   // 0x24-0x27
+        Mode.ZPG, Mode.ZPG, Mode.ZPG, Mode.ZPG,   // 0x24-0x27
         Mode.IMP, Mode.IMM, Mode.ACC, Mode.NUL,   // 0x28-0x2b
-        Mode.ABS, Mode.ABS, Mode.ABS, Mode.NUL,   // 0x2c-0x2f
-        Mode.REL, Mode.INY, Mode.NUL, Mode.NUL,   // 0x30-0x33
-        Mode.NUL, Mode.ZPX, Mode.ZPX, Mode.NUL,   // 0x34-0x37
-        Mode.IMP, Mode.ABY, Mode.NUL, Mode.NUL,   // 0x38-0x3b
-        Mode.NUL, Mode.ABX, Mode.ABX, Mode.NUL,   // 0x3c-0x3f
+        Mode.ABS, Mode.ABS, Mode.ABS, Mode.ZPR,   // 0x2c-0x2f
+        Mode.REL, Mode.INY, Mode.ZPI, Mode.NUL,   // 0x30-0x33
+        Mode.ZPX, Mode.ZPX, Mode.ZPX, Mode.ZPG,   // 0x34-0x37
+        Mode.IMP, Mode.ABY, Mode.IMP, Mode.NUL,   // 0x38-0x3b
+        Mode.NUL, Mode.ABX, Mode.ABX, Mode.ZPR,   // 0x3c-0x3f
         Mode.IMP, Mode.XIN, Mode.NUL, Mode.NUL,   // 0x40-0x43
-        Mode.NUL, Mode.ZPG, Mode.ZPG, Mode.NUL,   // 0x44-0x47
+        Mode.NUL, Mode.ZPG, Mode.ZPG, Mode.ZPG,   // 0x44-0x47
         Mode.IMP, Mode.IMM, Mode.ACC, Mode.NUL,   // 0x48-0x4b
-        Mode.ABS, Mode.ABS, Mode.ABS, Mode.NUL,   // 0x4c-0x4f
-        Mode.REL, Mode.INY, Mode.NUL, Mode.NUL,   // 0x50-0x53
-        Mode.NUL, Mode.ZPX, Mode.ZPX, Mode.NUL,   // 0x54-0x57
-        Mode.IMP, Mode.ABY, Mode.NUL, Mode.NUL,   // 0x58-0x5b
-        Mode.NUL, Mode.ABX, Mode.ABX, Mode.NUL,   // 0x5c-0x5f
+        Mode.ABS, Mode.ABS, Mode.ABS, Mode.ZPR,   // 0x4c-0x4f
+        Mode.REL, Mode.INY, Mode.ZPI, Mode.NUL,   // 0x50-0x53
+        Mode.NUL, Mode.ZPX, Mode.ZPX, Mode.ZPG,   // 0x54-0x57
+        Mode.IMP, Mode.ABY, Mode.IMP, Mode.NUL,   // 0x58-0x5b
+        Mode.NUL, Mode.ABX, Mode.ABX, Mode.ZPR,   // 0x5c-0x5f
         Mode.IMP, Mode.XIN, Mode.NUL, Mode.NUL,   // 0x60-0x63
-        Mode.NUL, Mode.ZPG, Mode.ZPG, Mode.NUL,   // 0x64-0x67
+        Mode.ZPG, Mode.ZPG, Mode.ZPG, Mode.ZPG,   // 0x64-0x67
         Mode.IMP, Mode.IMM, Mode.ACC, Mode.NUL,   // 0x68-0x6b
-        Mode.IND, Mode.ABS, Mode.ABS, Mode.NUL,   // 0x6c-0x6f
-        Mode.REL, Mode.INY, Mode.NUL, Mode.NUL,   // 0x70-0x73
-        Mode.NUL, Mode.ZPX, Mode.ZPX, Mode.NUL,   // 0x74-0x77
-        Mode.IMP, Mode.ABY, Mode.NUL, Mode.NUL,   // 0x78-0x7b
-        Mode.NUL, Mode.ABX, Mode.ABX, Mode.NUL,   // 0x7c-0x7f
+        Mode.IND, Mode.ABS, Mode.ABS, Mode.ZPR,   // 0x6c-0x6f
+        Mode.REL, Mode.INY, Mode.ZPI, Mode.NUL,   // 0x70-0x73
+        Mode.ZPX, Mode.ZPX, Mode.ZPX, Mode.ZPG,   // 0x74-0x77
+        Mode.IMP, Mode.ABY, Mode.IMP, Mode.NUL,   // 0x78-0x7b
+        Mode.AIX, Mode.ABX, Mode.ABX, Mode.ZPR,   // 0x7c-0x7f
         Mode.REL, Mode.XIN, Mode.NUL, Mode.NUL,   // 0x80-0x83
-        Mode.ZPG, Mode.ZPG, Mode.ZPG, Mode.NUL,   // 0x84-0x87
-        Mode.IMP, Mode.NUL, Mode.IMP, Mode.NUL,   // 0x88-0x8b
-        Mode.ABS, Mode.ABS, Mode.ABS, Mode.NUL,   // 0x8c-0x8f
-        Mode.REL, Mode.INY, Mode.NUL, Mode.NUL,   // 0x90-0x93
-        Mode.ZPX, Mode.ZPX, Mode.ZPY, Mode.NUL,   // 0x94-0x97
+        Mode.ZPG, Mode.ZPG, Mode.ZPG, Mode.ZPG,   // 0x84-0x87
+        Mode.IMP, Mode.IMM, Mode.IMP, Mode.NUL,   // 0x88-0x8b
+        Mode.ABS, Mode.ABS, Mode.ABS, Mode.ZPR,   // 0x8c-0x8f
+        Mode.REL, Mode.INY, Mode.ZPI, Mode.NUL,   // 0x90-0x93
+        Mode.ZPX, Mode.ZPX, Mode.ZPY, Mode.ZPG,   // 0x94-0x97
         Mode.IMP, Mode.ABY, Mode.IMP, Mode.NUL,   // 0x98-0x9b
-        Mode.NUL, Mode.ABX, Mode.NUL, Mode.NUL,   // 0x9c-0x9f
+        Mode.ABS, Mode.ABX, Mode.ABX, Mode.ZPR,   // 0x9c-0x9f
         Mode.IMM, Mode.XIN, Mode.IMM, Mode.NUL,   // 0xa0-0xa3
-        Mode.ZPG, Mode.ZPG, Mode.ZPG, Mode.NUL,   // 0xa4-0xa7
+        Mode.ZPG, Mode.ZPG, Mode.ZPG, Mode.ZPG,   // 0xa4-0xa7
         Mode.IMP, Mode.IMM, Mode.IMP, Mode.NUL,   // 0xa8-0xab
-        Mode.ABS, Mode.ABS, Mode.ABS, Mode.NUL,   // 0xac-0xaf
-        Mode.REL, Mode.INY, Mode.NUL, Mode.NUL,   // 0xb0-0xb3
-        Mode.ZPX, Mode.ZPX, Mode.ZPY, Mode.NUL,   // 0xb4-0xb7
+        Mode.ABS, Mode.ABS, Mode.ABS, Mode.ZPR,   // 0xac-0xaf
+        Mode.REL, Mode.INY, Mode.ZPI, Mode.NUL,   // 0xb0-0xb3
+        Mode.ZPX, Mode.ZPX, Mode.ZPY, Mode.ZPG,   // 0xb4-0xb7
         Mode.IMP, Mode.ABY, Mode.IMP, Mode.NUL,   // 0xb8-0xbb
-        Mode.ABX, Mode.ABX, Mode.ABY, Mode.NUL,   // 0xbc-0xbf
+        Mode.ABX, Mode.ABX, Mode.ABY, Mode.ZPR,   // 0xbc-0xbf
         Mode.IMM, Mode.XIN, Mode.NUL, Mode.NUL,   // 0xc0-0xc3
-        Mode.ZPG, Mode.ZPG, Mode.ZPG, Mode.NUL,   // 0xc4-0xc7
+        Mode.ZPG, Mode.ZPG, Mode.ZPG, Mode.ZPG,   // 0xc4-0xc7
         Mode.IMP, Mode.IMM, Mode.IMP, Mode.NUL,   // 0xc8-0xcb
-        Mode.ABS, Mode.ABS, Mode.ABS, Mode.NUL,   // 0xcc-0xcf
-        Mode.REL, Mode.INY, Mode.NUL, Mode.NUL,   // 0xd0-0xd3
-        Mode.NUL, Mode.ZPX, Mode.ZPX, Mode.NUL,   // 0xd4-0xd7
-        Mode.IMP, Mode.ABY, Mode.NUL, Mode.NUL,   // 0xd8-0xdb
-        Mode.NUL, Mode.ABX, Mode.ABX, Mode.NUL,   // 0xdc-0xdf
+        Mode.ABS, Mode.ABS, Mode.ABS, Mode.ZPR,   // 0xcc-0xcf
+        Mode.REL, Mode.INY, Mode.ZPI, Mode.NUL,   // 0xd0-0xd3
+        Mode.NUL, Mode.ZPX, Mode.ZPX, Mode.ZPG,   // 0xd4-0xd7
+        Mode.IMP, Mode.ABY, Mode.IMP, Mode.NUL,   // 0xd8-0xdb
+        Mode.NUL, Mode.ABX, Mode.ABX, Mode.ZPR,   // 0xdc-0xdf
         Mode.IMM, Mode.XIN, Mode.NUL, Mode.NUL,   // 0xe0-0xe3
-        Mode.ZPG, Mode.ZPG, Mode.ZPG, Mode.NUL,   // 0xe4-0xe7
+        Mode.ZPG, Mode.ZPG, Mode.ZPG, Mode.ZPG,   // 0xe4-0xe7
         Mode.IMP, Mode.IMM, Mode.IMP, Mode.NUL,   // 0xe8-0xeb
-        Mode.ABS, Mode.ABS, Mode.ABS, Mode.NUL,   // 0xec-0xef
-        Mode.REL, Mode.INY, Mode.NUL, Mode.NUL,   // 0xf0-0xf3
-        Mode.NUL, Mode.ZPX, Mode.ZPX, Mode.NUL,   // 0xf4-0xf7
-        Mode.IMP, Mode.ABY, Mode.NUL, Mode.NUL,   // 0xf8-0xfb
-        Mode.NUL, Mode.ABX, Mode.ABX, Mode.NUL    // 0xfc-0xff
+        Mode.ABS, Mode.ABS, Mode.ABS, Mode.ZPR,   // 0xec-0xef
+        Mode.REL, Mode.INY, Mode.ZPI, Mode.NUL,   // 0xf0-0xf3
+        Mode.NUL, Mode.ZPX, Mode.ZPX, Mode.ZPG,   // 0xf4-0xf7
+        Mode.IMP, Mode.ABY, Mode.IMP, Mode.NUL,   // 0xf8-0xfb
+        Mode.NUL, Mode.ABX, Mode.ABX, Mode.ZPR    // 0xfc-0xff
     };
 
 
     /**
-     * Size, in bytes, required for each instruction.
+     * Size, in bytes, required for each instruction. This table
+     * includes sizes for all instructions for NMOS 6502, CMOS 65C02,
+     * and CMOS 65C816
      */
-    public static final int[] instructionSizes = {
-        1, 2, 0, 0, 0, 2, 2, 0, 1, 2, 1, 0, 0, 3, 3, 0,
-        2, 2, 0, 0, 0, 2, 2, 0, 1, 3, 0, 0, 0, 3, 3, 0,
-        3, 2, 0, 0, 2, 2, 2, 0, 1, 2, 1, 0, 3, 3, 3, 0,
-        2, 2, 0, 0, 0, 2, 2, 0, 1, 3, 0, 0, 0, 3, 3, 0,
-        1, 2, 0, 0, 0, 2, 2, 0, 1, 2, 1, 0, 3, 3, 3, 0,
-        2, 2, 0, 0, 0, 2, 2, 0, 1, 3, 0, 0, 0, 3, 3, 0,
-        1, 2, 0, 0, 0, 2, 2, 0, 1, 2, 1, 0, 3, 3, 3, 0,
-        2, 2, 0, 0, 0, 2, 2, 0, 1, 3, 0, 0, 0, 3, 3, 0,
-        2, 2, 0, 0, 2, 2, 2, 0, 1, 0, 1, 0, 3, 3, 3, 0,
-        2, 2, 0, 0, 2, 2, 2, 0, 1, 3, 1, 0, 0, 3, 0, 0,
-        2, 2, 2, 0, 2, 2, 2, 0, 1, 2, 1, 0, 3, 3, 3, 0,
-        2, 2, 0, 0, 2, 2, 2, 0, 1, 3, 1, 0, 3, 3, 3, 0,
-        2, 2, 0, 0, 2, 2, 2, 0, 1, 2, 1, 0, 3, 3, 3, 0,
-        2, 2, 0, 0, 0, 2, 2, 0, 1, 3, 0, 0, 0, 3, 3, 0,
-        2, 2, 0, 0, 2, 2, 2, 0, 1, 2, 1, 0, 3, 3, 3, 0,
-        2, 2, 0, 0, 0, 2, 2, 0, 1, 3, 0, 0, 0, 3, 3, 0
+    int[] instructionSizes = {
+        1, 2, 2, 1, 2, 2, 2, 2, 1, 2, 1, 1, 3, 3, 3, 3,   // 0x00-0x0f
+        2, 2, 2, 1, 2, 2, 2, 2, 1, 3, 1, 1, 3, 3, 3, 3,   // 0x10-0x1f
+        3, 2, 2, 1, 2, 2, 2, 2, 1, 2, 1, 1, 3, 3, 3, 3,   // 0x20-0x2f
+        2, 2, 2, 1, 2, 2, 2, 2, 1, 3, 1, 1, 3, 3, 3, 3,   // 0x30-0x3f
+        1, 2, 2, 1, 2, 2, 2, 2, 1, 2, 1, 1, 3, 3, 3, 3,   // 0x40-0x4f
+        2, 2, 2, 1, 2, 2, 2, 2, 1, 3, 1, 1, 3, 3, 3, 3,   // 0x50-0x5f
+        1, 2, 2, 1, 2, 2, 2, 2, 1, 2, 1, 1, 3, 3, 3, 3,   // 0x60-0x6f
+        2, 2, 2, 1, 2, 2, 2, 2, 1, 3, 1, 1, 3, 3, 3, 3,   // 0x70-0x7f
+        2, 2, 2, 1, 2, 2, 2, 2, 1, 2, 1, 1, 3, 3, 3, 3,   // 0x80-0x8f
+        2, 2, 2, 1, 2, 2, 2, 2, 1, 3, 1, 1, 3, 3, 3, 3,   // 0x90-0x9f
+        2, 2, 2, 1, 2, 2, 2, 2, 1, 2, 1, 1, 3, 3, 3, 3,   // 0xa0-0xaf
+        2, 2, 2, 1, 2, 2, 2, 2, 1, 3, 1, 1, 3, 3, 3, 3,   // 0xb0-0xbf
+        2, 2, 2, 1, 2, 2, 2, 2, 1, 2, 1, 1, 3, 3, 3, 3,   // 0xc0-0xcf
+        2, 2, 2, 1, 2, 2, 2, 2, 1, 3, 1, 1, 3, 3, 3, 3,   // 0xd0-0xdf
+        2, 2, 2, 1, 2, 2, 2, 2, 1, 2, 1, 1, 3, 3, 3, 3,   // 0xe0-0xef
+        2, 2, 2, 1, 2, 2, 2, 2, 1, 3, 1, 1, 3, 3, 3, 3    // 0xf0-0xff
     };
 
     /**
-     * Number of clock cycles required for each instruction
+     * Number of clock cycles required for each instruction when
+     * in NMOS mode.
      */
-    public static final int[] instructionClocks = {
-        7, 6, 0, 0, 0, 3, 5, 0, 3, 2, 2, 0, 0, 4, 6, 0,
-        2, 5, 0, 0, 0, 4, 6, 0, 2, 4, 0, 0, 0, 4, 7, 0,
-        6, 6, 0, 0, 3, 3, 5, 0, 4, 2, 2, 0, 4, 4, 6, 0,
-        2, 5, 0, 0, 0, 4, 6, 0, 2, 4, 0, 0, 0, 4, 7, 0,
-        6, 6, 0, 0, 0, 3, 5, 0, 3, 2, 2, 0, 3, 4, 6, 0,
-        2, 5, 0, 0, 0, 4, 6, 0, 2, 4, 0, 0, 0, 4, 7, 0,
-        6, 6, 0, 0, 0, 3, 5, 0, 4, 2, 2, 0, 5, 4, 6, 0,
-        2, 5, 0, 0, 0, 4, 6, 0, 2, 4, 0, 0, 0, 4, 7, 0,
-        2, 6, 0, 0, 3, 3, 3, 0, 2, 0, 2, 0, 4, 4, 4, 0,
-        2, 6, 0, 0, 4, 4, 4, 0, 2, 5, 2, 0, 0, 5, 0, 0,
-        2, 6, 2, 0, 3, 3, 3, 0, 2, 2, 2, 0, 4, 4, 4, 0,
-        2, 5, 0, 0, 4, 4, 4, 0, 2, 4, 2, 0, 4, 4, 4, 0,
-        2, 6, 0, 0, 3, 3, 5, 0, 2, 2, 2, 0, 4, 4, 6, 0,
-        2, 5, 0, 0, 0, 4, 6, 0, 2, 4, 0, 0, 0, 4, 7, 0,
-        2, 6, 0, 0, 3, 3, 5, 0, 2, 2, 2, 0, 4, 4, 6, 0,
-        2, 5, 0, 0, 0, 4, 6, 0, 2, 4, 0, 0, 0, 4, 7, 0
+    int[] instructionClocksNmos = {
+        7, 6, 1, 8, 3, 3, 5, 5, 3, 2, 2, 2, 4, 4, 6, 6,   // 0x00-0x0f
+        2, 5, 1, 8, 4, 4, 6, 6, 2, 4, 2, 7, 4, 4, 7, 7,   // 0x10-0x1f
+        6, 6, 1, 8, 3, 3, 5, 5, 4, 2, 2, 2, 4, 4, 6, 6,   // 0x20-0x2f
+        2, 5, 1, 8, 4, 4, 6, 6, 2, 4, 2, 7, 4, 4, 7, 7,   // 0x30-0x3f
+        6, 6, 1, 8, 3, 3, 5, 5, 3, 2, 2, 2, 3, 4, 6, 6,   // 0x40-0x4f
+        2, 5, 1, 8, 4, 4, 6, 6, 2, 4, 2, 7, 4, 4, 7, 7,   // 0x50-0x5f
+        6, 6, 1, 8, 3, 3, 5, 5, 4, 2, 2, 2, 5, 4, 6, 6,   // 0x60-0x6f
+        2, 5, 1, 8, 4, 4, 6, 6, 2, 4, 2, 7, 4, 4, 7, 7,   // 0x70-0x7f
+        2, 6, 2, 6, 3, 3, 3, 3, 2, 2, 2, 2, 4, 4, 4, 4,   // 0x80-0x8f
+        2, 6, 1, 6, 4, 4, 4, 4, 2, 5, 2, 5, 5, 5, 5, 5,   // 0x90-0x9f
+        2, 6, 2, 6, 3, 3, 3, 3, 2, 2, 2, 2, 4, 4, 4, 4,   // 0xa0-0xaf
+        2, 5, 1, 5, 4, 4, 4, 4, 2, 4, 2, 4, 4, 4, 4, 4,   // 0xb0-0xbf
+        2, 6, 2, 8, 3, 3, 5, 5, 2, 2, 2, 2, 4, 4, 6, 6,   // 0xc0-0xcf
+        2, 5, 1, 8, 4, 4, 6, 6, 2, 4, 2, 7, 4, 4, 7, 7,   // 0xd0-0xdf
+        2, 6, 2, 8, 3, 3, 5, 5, 2, 2, 2, 2, 4, 4, 6, 6,   // 0xe0-0xef
+        2, 5, 1, 8, 4, 4, 6, 6, 2, 4, 2, 7, 4, 4, 7, 7    // 0xf0-0xff
+    };
+
+    /**
+     * Number of clock cycles required for each instruction when
+     * in CMOS mode
+     */
+    int[] instructionClocksCmos = {
+        7, 6, 2, 1, 5, 3, 5, 5, 3, 2, 2, 1, 6, 4, 6, 5,   // 0x00-0x0f
+        2, 5, 5, 1, 5, 4, 6, 5, 2, 4, 2, 1, 6, 4, 6, 5,   // 0x10-0x1f
+        6, 6, 2, 1, 3, 3, 5, 5, 4, 2, 2, 1, 4, 4, 6, 5,   // 0x20-0x2f
+        2, 5, 5, 1, 4, 4, 6, 5, 2, 4, 2, 1, 4, 4, 6, 5,   // 0x30-0x3f
+        6, 6, 2, 1, 2, 3, 5, 3, 3, 2, 2, 1, 3, 4, 6, 5,   // 0x40-0x4f
+        2, 5, 5, 1, 4, 4, 6, 5, 2, 4, 3, 1, 8, 4, 6, 5,   // 0x50-0x5f
+        6, 6, 2, 1, 3, 3, 5, 5, 4, 2, 2, 1, 6, 4, 6, 5,   // 0x60-0x6f
+        2, 5, 5, 1, 4, 4, 6, 5, 2, 4, 4, 3, 6, 4, 6, 5,   // 0x70-0x7f
+        3, 6, 2, 1, 3, 3, 3, 5, 2, 2, 2, 1, 4, 4, 4, 5,   // 0x80-0x8f
+        2, 6, 5, 1, 4, 4, 4, 5, 2, 5, 2, 1, 4, 5, 5, 5,   // 0x90-0x9f
+        2, 6, 2, 1, 3, 3, 3, 5, 2, 2, 2, 1, 4, 4, 4, 5,   // 0xa0-0xaf
+        2, 5, 5, 1, 4, 4, 4, 5, 2, 4, 2, 1, 4, 4, 4, 5,   // 0xb0-0xbf
+        2, 6, 2, 1, 3, 3, 5, 5, 2, 2, 2, 3, 4, 4, 6, 5,   // 0xc0-0xcf
+        2, 5, 5, 1, 4, 4, 6, 5, 2, 4, 3, 3, 4, 4, 7, 5,   // 0xd0-0xdf
+        2, 6, 2, 1, 3, 3, 5, 5, 2, 2, 2, 1, 4, 4, 6, 5,   // 0xe0-0xef
+        2, 5, 5, 1, 4, 4, 6, 5, 2, 4, 4, 1, 4, 4, 7, 5    // 0xf0-0xff
     };
 
 }

src/main/java/com/loomcom/symon/Main.java

@@ -0,0 +1,160 @@
+/*
+ * Copyright (c) 2008-2025 Seth J. Morabito <web@loomcom.com>
+ *                         Maik Merten <maikmerten@googlemail.com>
+ *
+ * Permission is hereby granted, free of charge, to any person obtaining
+ * a copy of this software and associated documentation files (the
+ * "Software"), to deal in the Software without restriction, including
+ * without limitation the rights to use, copy, modify, merge, publish,
+ * distribute, sublicense, and/or sell copies of the Software, and to
+ * permit persons to whom the Software is furnished to do so, subject to
+ * the following conditions:
+ *
+ * The above copyright notice and this permission notice shall be
+ * included in all copies or substantial portions of the Software.
+ *
+ * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND,
+ * EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF
+ * MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND
+ * NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS BE
+ * LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION
+ * OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION
+ * WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.
+ */
+
+package com.loomcom.symon;
+
+import com.loomcom.symon.machines.*;
+import com.loomcom.symon.ui.Ui;
+
+import org.apache.commons.cli.*;
+import org.slf4j.Logger;
+import org.slf4j.LoggerFactory;
+
+import java.util.Locale;
+
+import javax.swing.SwingUtilities;
+
+public class Main {
+    private final static Logger logger = LoggerFactory.getLogger(Main.class.getName());
+
+    /**
+     * Main entry point to the simulator. Creates a simulator and shows the main
+     * window.
+     *
+     * @param args Program arguments
+     */
+    public static void main(String[] args) throws Exception {
+
+        Class<?> machineClass = null;
+
+        Options options = new Options();
+
+        options.addOption(new Option("h", "help", false, "Print this message."));
+        options.addOption(new Option("m", "machine", true, "Specify machine type."));
+        options.addOption(new Option("c", "cpu", true, "Specify CPU type."));
+        options.addOption(new Option("r", "rom", true, "Specify ROM file."));
+        options.addOption(new Option("b", "brk", false, "Halt on BRK"));
+
+        CommandLineParser parser = new DefaultParser();
+
+        try {
+
+            CommandLine line = parser.parse(options, args);
+            InstructionTable.CpuBehavior cpuBehavior = null;
+            String romFile = null;
+            boolean haltOnBreak = false;
+
+            if (line.hasOption("help")) {
+                HelpFormatter formatter = new HelpFormatter();
+                formatter.printHelp("symon", options, false);
+                return;
+            }
+
+            if (line.hasOption("machine")) {
+                String machine = line.getOptionValue("machine").toLowerCase(Locale.ENGLISH);
+                switch (machine) {
+                    case "multicomp":
+                        machineClass = MulticompMachine.class;
+                        break;
+                    case "simple":
+                        machineClass = SimpleMachine.class;
+                        break;
+                    case "symon":
+                        machineClass = SymonMachine.class;
+                        break;
+                    case "beneater":
+                        machineClass = BenEaterMachine.class;
+                        break;
+                    case "mike42":
+                        machineClass = MichaelBillingtonMachine.class;
+                        break;
+                    default:
+                        logger.error("Could not start Symon. Unknown machine type {}", machine);
+                        return;
+                }
+            }
+
+            if (line.hasOption("cpu")) {
+                String cpu = line.getOptionValue("cpu").toLowerCase(Locale.ENGLISH);
+                switch (cpu) {
+                    case "6502":
+                        cpuBehavior = InstructionTable.CpuBehavior.NMOS_6502;
+                        break;
+                    case "65c02":
+                        cpuBehavior = InstructionTable.CpuBehavior.CMOS_6502;
+                        break;
+                    case "65c816":
+                        cpuBehavior = InstructionTable.CpuBehavior.CMOS_65816;
+                        break;
+                    default:
+                        logger.error("Could not start Symon. Unknown cpu type {}", cpu);
+                        return;
+                }
+            }
+
+            if (line.hasOption("rom")) {
+                romFile = line.getOptionValue("rom");
+            }
+
+            if (line.hasOption("brk")) {
+                haltOnBreak = true;
+            }
+
+            Ui.initUi();
+
+            while (true) {
+                if (machineClass == null) {
+                    machineClass = Ui.showMachineSelectionDialog();
+                }
+
+                if (cpuBehavior == null) {
+                    cpuBehavior = InstructionTable.CpuBehavior.NMOS_6502;
+                }
+
+                final Simulator simulator = new Simulator(machineClass, cpuBehavior, romFile, haltOnBreak);
+
+                SwingUtilities.invokeLater(() -> {
+                    // Create the main UI window:
+                    try {
+                        simulator.createAndShowUi();
+                    } catch (Exception e) {
+                        logger.error("Error during Symon UI initialization: {}", e.getMessage());
+                        System.exit(-1);
+                    }
+                });
+
+                Simulator.MainCommand cmd = simulator.waitForCommand();
+
+                if (cmd.equals(Simulator.MainCommand.SELECTMACHINE)) {
+                    machineClass = null;
+                } else {
+                    break;
+                }
+            }
+        } catch (ParseException ex) {
+            logger.error("Could not start Symon. Reason: {}", ex.getMessage());
+        }
+    }
+
+}

src/main/java/com/loomcom/symon/MemoryRange.java

@@ -1,5 +1,5 @@
 /*
- * Copyright (c) 2008-2013 Seth J. Morabito <sethm@loomcom.com>
+ * Copyright (c) 2008-2025 Seth J. Morabito <web@loomcom.com>
  *
  * Permission is hereby granted, free of charge, to any person obtaining
  * a copy of this software and associated documentation files (the
@@ -27,84 +27,85 @@ import com.loomcom.symon.exceptions.*;
 
 /**
  * MemoryRange is a simple container class representing a literal
- * range of memory, with a staraddress, and an end address.  It has
+ * range of memory, with a start address, and an end address.  It has
  * guards against creating impossible memory ranges, and implements
  * some useful methods for checking address inclusion and range
  * overlaps.
  */
 public class MemoryRange implements Comparable<MemoryRange> {
 
-  /** The starting address of the memory range. */
-  public int startAddress;
-  /** The ending address of the memory range. */
-  public int endAddress;
+    /**
+     * The starting address of the memory range.
+     */
+    public int startAddress;
+    /**
+     * The ending address of the memory range.
+     */
+    public int endAddress;
 
-  public MemoryRange(int startAddress, int endAddress)
-		throws MemoryRangeException {
-    if (startAddress < 0 || endAddress < 0) {
-      throw new MemoryRangeException("Addresses cannot be less than 0.");
+    public MemoryRange(int startAddress, int endAddress)
+            throws MemoryRangeException {
+        if (startAddress < 0 || endAddress < 0) {
+            throw new MemoryRangeException("Addresses cannot be less than 0.");
+        }
+        if (startAddress >= endAddress) {
+            throw new MemoryRangeException("End address must be greater " +
+                    "than start address.");
+        }
+        this.startAddress = startAddress;
+        this.endAddress = endAddress;
     }
-    if (startAddress >= endAddress) {
-      throw new MemoryRangeException("End address must be greater " +
-                                     "than start address.");
+
+    /**
+     * @return the starting address.
+     */
+    public int startAddress() {
+        return startAddress;
     }
-    this.startAddress = startAddress;
-    this.endAddress = endAddress;
-  }
 
-  /**
-   * @returns the starting address.
-   */
-  public int startAddress() {
-    return startAddress;
-  }
-
-  /**
-   * @returns the ending address.
-   */
-  public int endAddress() {
-    return endAddress;
-  }
-
-  /**
-   * Checks for address inclusion in the range.
-   *
-   * @returns true if the address is included within this range,
-   *          false otherwise.
-   */
-  public boolean includes(int address) {
-    return (address <= endAddress &&
-            address >= startAddress);
-  }
-
-  /**
-   * Checks for overlapping memory ranges.
-   *
-   * @returns true if this range overlaps in any way with the other.
-   */
-  public boolean overlaps(MemoryRange other) {
-    return (this.includes(other.startAddress()) ||
-            other.includes(this.startAddress()));
-  }
-
-  // Implementation of Comparable interface
-  public int compareTo(MemoryRange other) {
-    if (other == null) {
-      throw new NullPointerException("Cannot compare to null.");
+    /**
+     * @return the ending address.
+     */
+    public int endAddress() {
+        return endAddress;
     }
-    if (this == other) {
-      return 0;
-    }
-    Integer thisStartAddr = new Integer(this.startAddress());
-    Integer thatStartAddr = new Integer(other.startAddress());
-    return thisStartAddr.compareTo(thatStartAddr);
-  }
 
-  public String toString() {
-    StringBuffer desc = new StringBuffer("@");
-    desc.append(String.format("0x%04x", startAddress));
-    desc.append("-");
-    desc.append(String.format("0x%04x", endAddress));
-    return desc.toString();
-  }
+    /**
+     * Checks for address inclusion in the range.
+     *
+     * @return true if the address is included within this range,
+     * false otherwise.
+     */
+    public boolean includes(int address) {
+        return (address <= endAddress &&
+                address >= startAddress);
+    }
+
+    /**
+     * Checks for overlapping memory ranges.
+     *
+     * @return true if this range overlaps in any way with the other.
+     */
+    public boolean overlaps(MemoryRange other) {
+        return (this.includes(other.startAddress()) ||
+                other.includes(this.startAddress()));
+    }
+
+    // Implementation of Comparable interface
+    public int compareTo(MemoryRange other) {
+        if (other == null) {
+            throw new NullPointerException("Cannot compare to null.");
+        }
+        if (this == other) {
+            return 0;
+        }
+        Integer thisStartAddr = this.startAddress();
+        Integer thatStartAddr = other.startAddress();
+        return thisStartAddr.compareTo(thatStartAddr);
+    }
+
+    public String toString() {
+        return "@" + String.format("0x%04x", startAddress) + "-" +
+                String.format("0x%04x", endAddress);
+    }
 }

src/main/java/com/loomcom/symon/Preferences.java

@@ -1,5 +1,5 @@
 /*
- * Copyright (c) 2008-2013 Seth J. Morabito <sethm@loomcom.com>
+ * Copyright (c) 2008-2025 Seth J. Morabito <web@loomcom.com>
  *
  * Permission is hereby granted, free of charge, to any person obtaining
  * a copy of this software and associated documentation files (the
@@ -27,15 +27,13 @@ import javax.swing.*;
 
 public interface Preferences {
 
-    public static final int DEFAULT_PROGRAM_LOAD_ADDRESS = 0x0300;
+    int DEFAULT_PROGRAM_LOAD_ADDRESS = 0x0300;
 
-    public static final boolean DEFAULT_HALT_ON_BREAK = true;
+    JDialog getDialog();
 
-    public JDialog getDialog();
+    int getProgramStartAddress();
 
-    public int getProgramStartAddress();
+    boolean getHaltOnBreak();
 
-    public boolean getHaltOnBreak();
-
-    public void updateUi();
+    void updateUi();
 }

src/main/java/com/loomcom/symon/devices/Acia.java

@@ -1,5 +1,5 @@
 /*
- * Copyright (c) 2008-2013 Seth J. Morabito <sethm@loomcom.com>
+ * Copyright (c) 2008-2025 Seth J. Morabito <web@loomcom.com>
  *
  * Permission is hereby granted, free of charge, to any person obtaining
  * a copy of this software and associated documentation files (the
@@ -23,169 +23,48 @@
 
 package com.loomcom.symon.devices;
 
-import com.loomcom.symon.exceptions.*;
-
-import java.util.logging.Level;
-import java.util.logging.Logger;
+import com.loomcom.symon.exceptions.MemoryRangeException;
 
 
 /**
- * This is a simulation of the MOS 6551 ACIA, with limited
- * functionality.  Interrupts are not supported.
- * <p/>
- * Unlike a 16550 UART, the 6551 ACIA has only one-byte transmit and
- * receive buffers. It is the programmer's responsibility to check the
- * status (full or empty) for transmit and receive buffers before
- * writing / reading.
+ * Abstract base class for ACIAS such as the 6551 and 6580
  */
-public class Acia extends Device {
 
-    public static final int ACIA_SIZE = 4;
+public abstract class Acia extends Device {
 
-    static final int DATA_REG = 0;
-    static final int STAT_REG = 1;
-    static final int CMND_REG = 2;
-    static final int CTRL_REG = 3;
+    private final String name;
 
     /**
      * Register addresses
      */
-    private int baseAddress;
+    int baseAddress;
 
-    /**
-     * Registers. These are ignored in the current implementation.
-     */
-    private int commandRegister;
-    private int controlRegister;
+    boolean receiveIrqEnabled = false;
+    boolean transmitIrqEnabled = false;
+    boolean overrun = false;
+    boolean interrupt = false;
 
-    private boolean overrun = false;
-
-    private long lastTxWrite   = 0;
-    private long lastRxRead    = 0;
-    private int  baudRate      = 0;
-    private long baudRateDelay = 0;
+    long lastTxWrite   = 0;
+    long lastRxRead    = 0;
+    int  baudRate      = 0;
+    long baudRateDelay = 0;
 
     /**
      * Read/Write buffers
      */
-    private int rxChar = 0;
-    private int txChar = 0;
+    int rxChar = 0;
+    int txChar = 0;
 
-    private boolean rxFull  = false;
-    private boolean txEmpty = true;
+    boolean rxFull  = false;
+    boolean txEmpty = true;
 
-    public Acia(int address) throws MemoryRangeException {
-        super(address, address + ACIA_SIZE - 1, "ACIA");
+
+    public Acia(int address, int size, String name) throws MemoryRangeException {
+        super(address, address + size - 1, name);
+        this.name = name;
         this.baseAddress = address;
     }
 
-    @Override
-    public int read(int address) throws MemoryAccessException {
-        switch (address) {
-            case DATA_REG:
-                return rxRead();
-            case STAT_REG:
-                return statusReg();
-            case CMND_REG:
-                return commandRegister;
-            case CTRL_REG:
-                return controlRegister;
-            default:
-                throw new MemoryAccessException("No register.");
-        }
-    }
-
-    @Override
-    public void write(int address, int data) throws MemoryAccessException {
-        switch (address) {
-            case 0:
-                txWrite(data);
-                break;
-            case 1:
-                reset();
-                break;
-            case 2:
-                commandRegister = data;
-                break;
-            case 3:
-                setControlRegister(data);
-                break;
-            default:
-                throw new MemoryAccessException("No register.");
-        }
-    }
-
-    /**
-     * Set the control register and associated state.
-     *
-     * @param data
-     */
-    public void setControlRegister(int data) {
-        this.controlRegister = data;
-
-        // If the value of the data is 0, this is a request to reset,
-        // otherwise it's a control update.
-
-        if (data == 0) {
-            reset();
-        } else {
-            // Mask the lower three bits to get the baud rate.
-            int baudSelector = data & 0x0f;
-            switch (baudSelector) {
-                case 0:
-                    baudRate = 0;
-                    break;
-                case 1:
-                    baudRate = 50;
-                    break;
-                case 2:
-                    baudRate = 75;
-                    break;
-                case 3:
-                    baudRate = 110; // Real rate is actually 109.92
-                    break;
-                case 4:
-                    baudRate = 135; // Real rate is actually 134.58
-                    break;
-                case 5:
-                    baudRate = 150;
-                    break;
-                case 6:
-                    baudRate = 300;
-                    break;
-                case 7:
-                    baudRate = 600;
-                    break;
-                case 8:
-                    baudRate = 1200;
-                    break;
-                case 9:
-                    baudRate = 1800;
-                    break;
-                case 10:
-                    baudRate = 2400;
-                    break;
-                case 11:
-                    baudRate = 3600;
-                    break;
-                case 12:
-                    baudRate = 4800;
-                    break;
-                case 13:
-                    baudRate = 7200;
-                    break;
-                case 14:
-                    baudRate = 9600;
-                    break;
-                case 15:
-                    baudRate = 19200;
-                    break;
-            }
-
-            // Recalculate the baud rate delay.
-            baudRateDelay = calculateBaudRateDelay();
-        }
-    }
 
     /*
      * Calculate the delay in nanoseconds between successive read/write operations, based on the
@@ -204,6 +83,7 @@ public class Acia extends Device {
     /**
      * @return The simulated baud rate in bps.
      */
+    @SuppressWarnings("unused")
     public int getBaudRate() {
         return baudRate;
     }
@@ -215,48 +95,59 @@ public class Acia extends Device {
      */
     public void setBaudRate(int rate) {
         this.baudRate = rate;
+		this.baudRateDelay = calculateBaudRateDelay();
     }
 
     /**
      * @return The contents of the status register.
      */
-    public int statusReg() {
-        // TODO: Overrun, Parity Error, Framing Error, DTR, DSR, and Interrupt flags.
-        int stat = 0;
-        if (rxFull && System.nanoTime() >= (lastRxRead + baudRateDelay)) {
-            stat |= 0x08;
-        }
-        if (txEmpty && System.nanoTime() >= (lastTxWrite + baudRateDelay)) {
-            stat |= 0x10;
-        }
-        return stat;
-    }
+    public abstract int statusReg(boolean cpuAccess);
 
     @Override
     public String toString() {
-        return "ACIA@" + String.format("%04X", baseAddress);
+        return name + "@" + String.format("%04X", baseAddress);
     }
 
-    public synchronized int rxRead() {
-        lastRxRead = System.nanoTime();
-        rxFull = false;
+    public synchronized int rxRead(boolean cpuAccess) {
+        if (cpuAccess) {
+            lastRxRead = System.nanoTime();
+            overrun = false;
+            rxFull = false;
+        }
         return rxChar;
     }
 
     public synchronized void rxWrite(int data) {
+        if (rxFull) {
+            overrun = true;
+        }
+
         rxFull = true;
+
+        if (receiveIrqEnabled) {
+            interrupt = true;
+            getBus().assertIrq();
+        }
+
         rxChar = data;
     }
 
-    public synchronized int txRead() {
-        txEmpty = true;
+    public synchronized int txRead(boolean cpuAccess) {
+        if (cpuAccess) {
+            txEmpty = true;
+
+            if (transmitIrqEnabled) {
+                interrupt = true;
+                getBus().assertIrq();
+            }
+        }
         return txChar;
     }
 
     public synchronized void txWrite(int data) {
         lastTxWrite = System.nanoTime();
-        txEmpty = false;
         txChar = data;
+        txEmpty = false;
     }
 
     /**
@@ -269,15 +160,9 @@ public class Acia extends Device {
     /**
      * @return true if there is character data in the RX register.
      */
+    @SuppressWarnings("unused")
     public boolean hasRxChar() {
         return rxFull;
     }
 
-    private synchronized void reset() {
-        txChar = 0;
-        txEmpty = true;
-        rxChar = 0;
-        rxFull = false;
-    }
-
 }

src/main/java/com/loomcom/symon/devices/Acia6551.java

@@ -0,0 +1,218 @@
+/*
+ * Copyright (c) 2008-2025 Seth J. Morabito <web@loomcom.com>
+ *
+ * Permission is hereby granted, free of charge, to any person obtaining
+ * a copy of this software and associated documentation files (the
+ * "Software"), to deal in the Software without restriction, including
+ * without limitation the rights to use, copy, modify, merge, publish,
+ * distribute, sublicense, and/or sell copies of the Software, and to
+ * permit persons to whom the Software is furnished to do so, subject to
+ * the following conditions:
+ *
+ * The above copyright notice and this permission notice shall be
+ * included in all copies or substantial portions of the Software.
+ *
+ * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND,
+ * EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF
+ * MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND
+ * NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS BE
+ * LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION
+ * OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION
+ * WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.
+ */
+
+package com.loomcom.symon.devices;
+
+import com.loomcom.symon.exceptions.MemoryAccessException;
+import com.loomcom.symon.exceptions.MemoryRangeException;
+
+/**
+ * This is a simulation of the MOS 6551 ACIA, with limited
+ * functionality.
+ * <p/>
+ * Unlike a 16550 UART, the 6551 ACIA has only one-byte transmit and
+ * receive buffers. It is the programmer's responsibility to check the
+ * status (full or empty) for transmit and receive buffers before
+ * writing / reading.
+ */
+public class Acia6551 extends Acia {
+
+    public static final int ACIA_SIZE = 4;
+
+    static final int DATA_REG = 0;
+    static final int STAT_REG = 1;
+    static final int CMND_REG = 2;
+    static final int CTRL_REG = 3;
+
+    /**
+     * Registers. These are ignored in the current implementation.
+     */
+    private int commandRegister;
+    private int controlRegister;
+
+
+    public Acia6551(int address) throws MemoryRangeException {
+        super(address, ACIA_SIZE, "ACIA");
+
+        // Figure 6 in the 6551 ACIA data sheet says the "hardware reset"
+        // state of the Control Register is all zeros.
+        setControlRegister(0b00000000);
+        // Figure 7 of the 6551 ACIA data sheet says the "hardware reset"
+        // state of the Command Register is zeros, but Transmitter Control
+        // is set to "interrupt disabled, ready to send".
+        setCommandRegister(0b00000010);
+    }
+
+    @Override
+    public int read(int address, boolean cpuAccess) throws MemoryAccessException {
+        switch (address) {
+            case DATA_REG:
+                return rxRead(cpuAccess);
+            case STAT_REG:
+                return statusReg(cpuAccess);
+            case CMND_REG:
+                return commandRegister;
+            case CTRL_REG:
+                return controlRegister;
+            default:
+                throw new MemoryAccessException("No register.");
+        }
+    }
+
+    @Override
+    public void write(int address, int data) throws MemoryAccessException {
+        switch (address) {
+            case DATA_REG:
+                txWrite(data);
+                break;
+            case STAT_REG:
+                reset();
+                break;
+            case CMND_REG:
+                setCommandRegister(data);
+                break;
+            case CTRL_REG:
+                setControlRegister(data);
+                break;
+            default:
+                throw new MemoryAccessException("No register.");
+        }
+    }
+
+
+    private void setCommandRegister(int data) {
+        commandRegister = data;
+
+        // Bit 1 controls receiver IRQ behavior
+        receiveIrqEnabled = (commandRegister & 0x02) == 0;
+        // Bits 2 & 3 controls transmit IRQ behavior
+        transmitIrqEnabled = (commandRegister & 0x08) == 0 && (commandRegister & 0x04) != 0;
+    }
+
+    /**
+     * Set the control register and associated state.
+     *
+     * @param data Data to write into the control register
+     */
+    private void setControlRegister(int data) {
+        controlRegister = data;
+        int rate = 0;
+
+        // Mask the lower four bits to get the baud rate.
+        int baudSelector = data & 0x0f;
+        switch (baudSelector) {
+            case 1:
+                rate = 50;
+                break;
+            case 2:
+                rate = 75;
+                break;
+            case 3:
+                rate = 110; // Real rate is actually 109.92
+                break;
+            case 4:
+                rate = 135; // Real rate is actually 134.58
+                break;
+            case 5:
+                rate = 150;
+                break;
+            case 6:
+                rate = 300;
+                break;
+            case 7:
+                rate = 600;
+                break;
+            case 8:
+                rate = 1200;
+                break;
+            case 9:
+                rate = 1800;
+                break;
+            case 10:
+                rate = 2400;
+                break;
+            case 11:
+                rate = 3600;
+                break;
+            case 12:
+                rate = 4800;
+                break;
+            case 13:
+                rate = 7200;
+                break;
+            case 14:
+                rate = 9600;
+                break;
+            case 15:
+                rate = 19200;
+                break;
+            default:
+                break;
+        }
+
+        setBaudRate(rate);
+    }
+
+
+    /**
+     * @return The contents of the status register.
+     */
+    @Override
+    public int statusReg(boolean cpuAccess) {
+        // TODO: Parity Error, Framing Error, DTR, and DSR flags.
+        int stat = 0;
+        if (rxFull && System.nanoTime() >= (lastRxRead + baudRateDelay)) {
+            stat |= 0x08;
+        }
+        if (txEmpty && System.nanoTime() >= (lastTxWrite + baudRateDelay)) {
+            stat |= 0x10;
+        }
+        if (overrun) {
+            stat |= 0x04;
+        }
+        if (interrupt) {
+            stat |= 0x80;
+        }
+
+        if (cpuAccess) {
+            interrupt = false;
+        }
+
+        return stat;
+    }
+
+
+    private synchronized void reset() {
+        // Figure 6 in the 6551 ACIA data sheet says the "program reset"
+        // event does not modify the control register.
+
+        // Figure 7 in the 6551 ACIA data sheet says the "program reset"
+        // event keeps the "parity check" configuration in the command
+        // register, but resets the other bits to defaults.
+        setCommandRegister((commandRegister & 0xe0) | 0x02);
+
+        // Figure 8 in the 6551 ACIA data sheet says the "program reset"
+        // event clears the "overrun" flag but otherwise has no effect.
+        overrun = false;
+    }
+}

src/main/java/com/loomcom/symon/devices/Acia6850.java

@@ -0,0 +1,131 @@
+/*
+ * Copyright (c) 2008-2025 Seth J. Morabito <web@loomcom.com>
+ *                         Maik Merten <maikmerten@googlemail.com>
+ *
+ * Permission is hereby granted, free of charge, to any person obtaining
+ * a copy of this software and associated documentation files (the
+ * "Software"), to deal in the Software without restriction, including
+ * without limitation the rights to use, copy, modify, merge, publish,
+ * distribute, sublicense, and/or sell copies of the Software, and to
+ * permit persons to whom the Software is furnished to do so, subject to
+ * the following conditions:
+ *
+ * The above copyright notice and this permission notice shall be
+ * included in all copies or substantial portions of the Software.
+ *
+ * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND,
+ * EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF
+ * MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND
+ * NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS BE
+ * LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION
+ * OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION
+ * WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.
+ */
+
+package com.loomcom.symon.devices;
+
+import com.loomcom.symon.exceptions.MemoryAccessException;
+import com.loomcom.symon.exceptions.MemoryRangeException;
+
+
+/**
+ * This is a simulation of the Motorola 6850 ACIA, with limited
+ * functionality.
+ * <p>
+ * Unlike a 16550 UART, the 6850 ACIA has only one-byte transmit and
+ * receive buffers. It is the programmer's responsibility to check the
+ * status (full or empty) for transmit and receive buffers before
+ * writing / reading.
+ */
+public class Acia6850 extends Acia {
+
+    public static final int ACIA_SIZE = 2;
+
+    static final int STAT_REG = 0;	// read-only
+    static final int CTRL_REG = 0;	// write-only
+
+    static final int RX_REG = 1;	// read-only
+    static final int TX_REG = 1;	// write-only
+
+    public Acia6850(int address) throws MemoryRangeException {
+        super(address, ACIA_SIZE, "ACIA6850");
+        setBaudRate(2400);
+    }
+
+    @Override
+    public int read(int address, boolean cpuAccess) throws MemoryAccessException {
+        switch (address) {
+            case RX_REG:
+                return rxRead(cpuAccess);
+            case STAT_REG:
+                return statusReg(cpuAccess);
+
+            default:
+                throw new MemoryAccessException("No register.");
+        }
+    }
+
+    @Override
+    public void write(int address, int data) throws MemoryAccessException {
+        switch (address) {
+            case TX_REG:
+                txWrite(data);
+                break;
+            case CTRL_REG:
+                setCommandRegister(data);
+                break;
+            default:
+                throw new MemoryAccessException("No register.");
+        }
+    }
+
+    private void setCommandRegister(int data) {
+        // Bits 0 & 1 control the master reset
+        if((data & 0x01) != 0 && (data & 0x02) != 0) {
+            reset();
+        }
+
+        // Bit 7 controls receiver IRQ behavior
+        receiveIrqEnabled = (data & 0x80) != 0;
+        // Bits 5 & 6 controls transmit IRQ behavior
+        transmitIrqEnabled = (data & 0x20) != 0 && (data & 0x40) == 0;
+    }
+
+
+
+    /**
+     * @return The contents of the status register.
+     */
+    @Override
+    public int statusReg(boolean cpuAccess) {
+        // TODO: Parity Error, Framing Error, DTR, and DSR flags.
+        int stat = 0;
+        if (rxFull && System.nanoTime() >= (lastRxRead + baudRateDelay)) {
+            stat |= 0x01;
+        }
+        if (txEmpty && System.nanoTime() >= (lastTxWrite + baudRateDelay)) {
+            stat |= 0x02;
+        }
+        if (overrun) {
+            stat |= 0x20;
+        }
+        if (interrupt) {
+            stat |= 0x80;
+        }
+
+        if (cpuAccess) {
+            interrupt = false;
+        }
+
+        return stat;
+    }
+
+
+    private synchronized void reset() {
+        overrun = false;
+        rxFull = false;
+        txEmpty = true;
+        interrupt = false;
+    }
+
+}

src/main/java/com/loomcom/symon/devices/Crtc.java

@@ -1,20 +1,35 @@
+/*
+ * Copyright (c) 2008-2025 Seth J. Morabito <web@loomcom.com>
+ *
+ * Permission is hereby granted, free of charge, to any person obtaining
+ * a copy of this software and associated documentation files (the
+ * "Software"), to deal in the Software without restriction, including
+ * without limitation the rights to use, copy, modify, merge, publish,
+ * distribute, sublicense, and/or sell copies of the Software, and to
+ * permit persons to whom the Software is furnished to do so, subject to
+ * the following conditions:
+ *
+ * The above copyright notice and this permission notice shall be
+ * included in all copies or substantial portions of the Software.
+ *
+ * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND,
+ * EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF
+ * MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND
+ * NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS BE
+ * LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION
+ * OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION
+ * WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.
+ */
+
 package com.loomcom.symon.devices;
 
 import com.loomcom.symon.exceptions.MemoryAccessException;
 import com.loomcom.symon.exceptions.MemoryRangeException;
 
-import java.io.IOException;
-import java.util.logging.Logger;
-
-
 /**
  * Simulation of a 6545 CRTC and virtual CRT output.
  */
 public class Crtc extends Device {
-
-    private static final Logger logger = Logger.getLogger(Crtc.class.getName());
-
-
     // Memory locations in the CRTC address space
     public static final int REGISTER_SELECT          = 0;
     public static final int REGISTER_RW              = 1;
@@ -65,9 +80,14 @@ public class Crtc extends Device {
 
     private int currentRegister = 0;
 
-    private Memory memory;
+    // Status bits
+    private boolean rowColumnAddressing = false;
+    private boolean displayEnableSkew = false;
+    private boolean cursorSkew = false;
 
-    public Crtc(int deviceAddress, Memory memory) throws MemoryRangeException, IOException {
+    private final Memory memory;
+
+    public Crtc(int deviceAddress, Memory memory) throws MemoryRangeException {
         super(deviceAddress, deviceAddress + 2, "CRTC");
         this.memory = memory;
 
@@ -97,20 +117,18 @@ public class Crtc extends Device {
     }
 
     @Override
-    public int read(int address) throws MemoryAccessException {
-        switch (address) {
-            case REGISTER_RW:
-                switch (currentRegister) {
-                    case CURSOR_POSITION_LOW:
-                        return cursorPosition & 0xff;
-                    case CURSOR_POSITION_HIGH:
-                        return cursorPosition >> 8;
-                    default:
-                        return 0;
-                }
-            default:
-                return 0;
+    public int read(int address, boolean cpuAccess) throws MemoryAccessException {
+        if (address == REGISTER_RW) {
+            switch (currentRegister) {
+                case CURSOR_POSITION_LOW:
+                    return cursorPosition & 0xff;
+                case CURSOR_POSITION_HIGH:
+                    return cursorPosition >> 8;
+                default:
+                    return 0;
+            }
         }
+        return 0;
     }
 
     @Override
@@ -118,8 +136,9 @@ public class Crtc extends Device {
         return null;
     }
 
-    public int[] getDmaAccess() {
-        return memory.getDmaAccess();
+    public int getCharAtAddress(int address) throws MemoryAccessException {
+        // TODO: Row/Column addressing
+        return memory.read(address, false);
     }
 
     public int getHorizontalDisplayed() {
@@ -162,6 +181,18 @@ public class Crtc extends Device {
         return pageSize;
     }
 
+    public boolean getRowColumnAddressing() {
+        return rowColumnAddressing;
+    }
+
+    public boolean getDisplayEnableSkew() {
+        return displayEnableSkew;
+    }
+
+    public boolean getCursorSkew() {
+        return cursorSkew;
+    }
+
     private void setCurrentRegister(int registerNumber) {
         this.currentRegister = registerNumber;
     }
@@ -180,7 +211,9 @@ public class Crtc extends Device {
                 pageSize = horizontalDisplayed * verticalDisplayed;
                 break;
             case MODE_CONTROL:
-                // TODO: Implement multiple addressing modes and cursor skew.
+                rowColumnAddressing = (data & 0x04) != 0;
+                displayEnableSkew = (data & 0x10) != 0;
+                cursorSkew = (data & 0x20) != 0;
                 break;
             case SCAN_LINE:
                 scanLinesPerRow = data;

src/main/java/com/loomcom/symon/devices/Device.java

@@ -1,5 +1,5 @@
 /*
- * Copyright (c) 2008-2013 Seth J. Morabito <sethm@loomcom.com>
+ * Copyright (c) 2008-2025 Seth J. Morabito <web@loomcom.com>
  *
  * Permission is hereby granted, free of charge, to any person obtaining
  * a copy of this software and associated documentation files (the
@@ -45,7 +45,7 @@ public abstract class Device implements Comparable<Device> {
     /**
      * The memory range for this device.
      */
-    private MemoryRange memoryRange;
+    private final MemoryRange memoryRange;
 
     /**
      * The name of the device.
@@ -60,24 +60,19 @@ public abstract class Device implements Comparable<Device> {
     /**
      * Listeners to notify on update.
      */
-    private Set<DeviceChangeListener> deviceChangeListeners;
+    private final Set<DeviceChangeListener> deviceChangeListeners;
 
-    public Device(int startAddress, int endAddress, String name)
-            throws MemoryRangeException {
+    public Device(int startAddress, int endAddress, String name) throws MemoryRangeException {
         this.memoryRange = new MemoryRange(startAddress, endAddress);
         this.size = endAddress - startAddress + 1;
         this.name = name;
-        this.deviceChangeListeners = new HashSet<DeviceChangeListener>();
-    }
-
-    public Device(int startAddress, int endAddress) throws MemoryRangeException {
-        this(startAddress, endAddress, null);
+        this.deviceChangeListeners = new HashSet<>();
     }
 
     /* Methods required to be implemented by inheriting classes. */
     public abstract void write(int address, int data) throws MemoryAccessException;
 
-    public abstract int read(int address) throws MemoryAccessException;
+    public abstract int read(int address, boolean cpuAccess) throws MemoryAccessException;
 
     public abstract String toString();
 
@@ -97,6 +92,7 @@ public abstract class Device implements Comparable<Device> {
         return memoryRange.endAddress();
     }
 
+    @SuppressWarnings("unused")
     public int startAddress() {
         return memoryRange.startAddress();
     }
@@ -105,6 +101,7 @@ public abstract class Device implements Comparable<Device> {
         return name;
     }
 
+    @SuppressWarnings("unused")
     public void setName(String name) {
         this.name = name;
     }
@@ -118,8 +115,8 @@ public abstract class Device implements Comparable<Device> {
     }
 
     public void notifyListeners() {
-        for (DeviceChangeListener l : deviceChangeListeners) {
-            l.deviceStateChanged();
+        for (DeviceChangeListener listener : deviceChangeListeners) {
+            listener.deviceStateChanged();
         }
     }
 

src/main/java/com/loomcom/symon/devices/DeviceChangeListener.java

@@ -1,5 +1,5 @@
 /*
- * Copyright (c) 2013 Seth J. Morabito <web@loomcom.com>
+ * Copyright (c) 2008-2025 Seth J. Morabito <web@loomcom.com>
  *
  * Permission is hereby granted, free of charge, to any person obtaining
  * a copy of this software and associated documentation files (the
@@ -24,5 +24,5 @@
 package com.loomcom.symon.devices;
 
 public interface DeviceChangeListener {
-    public void deviceStateChanged();
+    void deviceStateChanged();
 }

src/main/java/com/loomcom/symon/devices/Memory.java

@@ -1,5 +1,5 @@
 /*
- * Copyright (c) 2008-2013 Seth J. Morabito <sethm@loomcom.com>
+ * Copyright (c) 2008-2025 Seth J. Morabito <web@loomcom.com>
  *
  * Permission is hereby granted, free of charge, to any person obtaining
  * a copy of this software and associated documentation files (the
@@ -28,12 +28,10 @@ import java.util.*;
 
 import com.loomcom.symon.exceptions.*;
 
-import javax.swing.*;
-
 public class Memory extends Device {
 
-    private boolean readOnly;
-    private int[] mem;
+    private final boolean readOnly;
+    private final int[] mem;
 
     /* Initialize all locations to 0x00 (BRK) */
     private static final int DEFAULT_FILL = 0x00;
@@ -57,8 +55,7 @@ public class Memory extends Device {
     }
 
     public static Memory makeRAM(int startAddress, int endAddress) throws MemoryRangeException {
-        Memory memory = new Memory(startAddress, endAddress, false);
-        return memory;
+        return new Memory(startAddress, endAddress, false);
     }
 
     public void write(int address, int data) throws MemoryAccessException {
@@ -97,7 +94,7 @@ public class Memory extends Device {
 
     }
 
-    public int read(int address) throws MemoryAccessException {
+    public int read(int address, boolean cpuAccess) throws MemoryAccessException {
         return this.mem[address];
     }
 
@@ -108,8 +105,4 @@ public class Memory extends Device {
     public String toString() {
         return "Memory: " + getMemoryRange().toString();
     }
-
-    public int[] getDmaAccess() {
-        return mem;
-    }
 }

src/main/java/com/loomcom/symon/devices/Pia.java

@@ -1,5 +1,5 @@
 /*
- * Copyright (c) 2008-2013 Seth J. Morabito <sethm@loomcom.com>
+ * Copyright (c) 2008-2025 Seth J. Morabito <web@loomcom.com>
  *
  * Permission is hereby granted, free of charge, to any person obtaining
  * a copy of this software and associated documentation files (the
@@ -23,45 +23,19 @@
 
 package com.loomcom.symon.devices;
 
-import com.loomcom.symon.exceptions.MemoryAccessException;
 import com.loomcom.symon.exceptions.MemoryRangeException;
 
-public class Via extends Device {
-    public static final int VIA_SIZE = 16;
+public abstract class Pia extends Device {
 
-    private static final int ORB = 0;
-    private static final int ORA = 1;
-    private static final int DDRB = 2;
-    private static final int DDRA = 3;
-    private static final int T1C_L = 4;
-    private static final int T1C_H = 5;
-    private static final int T1L_L = 6;
-    private static final int T1L_H = 7;
-    private static final int T2C_L = 8;
-    private static final int T2C_H = 9;
-    private static final int SR = 10;
-    private static final int ACR = 11;
-    private static final int PCR = 12;
-    private static final int IFR = 13;
-    private static final int IER = 14;
-    private static final int ORA_H = 15;
+    private final String name;
 
-    public Via(int address) throws MemoryRangeException {
-      super(address, address + VIA_SIZE - 1, "VIA");
-    }
-
-    @Override
-    public void write(int address, int data) throws MemoryAccessException {
-
-    }
-
-    @Override
-    public int read(int address) throws MemoryAccessException {
-        return 0;
+    public Pia(int startAddress, int endAddress, String name) throws MemoryRangeException {
+        super(startAddress, endAddress, name);
+        this.name = name;
     }
 
     @Override
     public String toString() {
-        return null;
+        return name;
     }
 }

src/main/java/com/loomcom/symon/devices/SdController.java

@@ -0,0 +1,213 @@
+/*
+ * Copyright (c) 2008-2025 Seth J. Morabito <web@loomcom.com>
+ *                         Maik Merten <maikmerten@googlemail.com>
+ *
+ * Permission is hereby granted, free of charge, to any person obtaining
+ * a copy of this software and associated documentation files (the
+ * "Software"), to deal in the Software without restriction, including
+ * without limitation the rights to use, copy, modify, merge, publish,
+ * distribute, sublicense, and/or sell copies of the Software, and to
+ * permit persons to whom the Software is furnished to do so, subject to
+ * the following conditions:
+ *
+ * The above copyright notice and this permission notice shall be
+ * included in all copies or substantial portions of the Software.
+ *
+ * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND,
+ * EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF
+ * MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND
+ * NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS BE
+ * LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION
+ * OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION
+ * WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.
+ */
+
+
+package com.loomcom.symon.devices;
+
+import com.loomcom.symon.exceptions.MemoryAccessException;
+import com.loomcom.symon.exceptions.MemoryRangeException;
+
+import java.io.File;
+import java.io.FileInputStream;
+import java.io.IOException;
+import java.io.RandomAccessFile;
+import java.util.logging.Level;
+import java.util.logging.Logger;
+
+/**
+ * Emulation for the SD-card controller of the MULTICOMP system.
+ * Neiter comlete nor correct.
+ */
+public class SdController extends Device {
+
+    private enum Status {
+        IDLE,
+        READ,
+        WRITE
+    }
+
+    public static final int CONTROLLER_SIZE = 8;
+    private final int SECTOR_SIZE = 512;
+    private final static Logger logger = Logger.getLogger(SdController.class.getName());
+
+    private File sdImageFile;
+    private int lba0, lba1, lba2;
+    private int position;
+    private Status status = Status.IDLE;
+
+    private final byte[] readBuffer = new byte[SECTOR_SIZE];
+    private final byte[] writeBuffer = new byte[SECTOR_SIZE];
+    private int readPosition = 0;
+    private int writePosition = 0;
+
+
+    public SdController(int address) throws MemoryRangeException {
+        super(address, address + CONTROLLER_SIZE - 1, "SDCONTROLLER");
+
+        sdImageFile = new File("sd.img");
+        if (!sdImageFile.exists()) {
+            sdImageFile = null;
+            logger.log(Level.INFO, "Could not find SD card image 'sd.img'");
+        }
+    }
+
+
+    @Override
+    public void write(int address, int data) throws MemoryAccessException {
+        switch (address) {
+            case 0:
+                writeData(data);
+                return;
+            case 1:
+                writeCommand(data);
+                return;
+            case 2:
+                this.lba0 = data;
+                return;
+            case 3:
+                this.lba1 = data;
+                return;
+            case 4:
+                this.lba2 = data;
+        }
+    }
+
+    @Override
+    public int read(int address, boolean cpuAccess) throws MemoryAccessException {
+        switch (address) {
+            case 0:
+                return readData();
+            case 1:
+                return readStatus();
+            default:
+                return 0;
+        }
+    }
+
+    private void computePosition() {
+        this.position = lba0 + (lba1 << 8) + (lba2 << 16);
+        // each sector is 512 bytes, so multiply accordingly
+        this.position <<= 9;
+    }
+
+    private void prepareRead() {
+        this.status = Status.READ;
+        this.readPosition = 0;
+        computePosition();
+
+        if (sdImageFile != null) {
+            try {
+                FileInputStream fis = new FileInputStream(sdImageFile);
+                long bytesSkipped = fis.skip(this.position);
+                if (bytesSkipped < this.position) {
+                    logger.log(Level.WARNING, "Failed to seek to position " + this.position);
+                }
+                int read = fis.read(readBuffer);
+                if (read < SECTOR_SIZE) {
+                    logger.log(Level.WARNING, "not enough data to fill read buffer from SD image file");
+                }
+                fis.close();
+            } catch (IOException ex) {
+                logger.log(Level.WARNING, "could not fill read buffer from SD image file", ex);
+            }
+        }
+    }
+
+    private void prepareWrite() {
+        this.status = Status.WRITE;
+        this.writePosition = 0;
+        computePosition();
+    }
+
+
+    private int readData() {
+        if (status != Status.READ) {
+            return 0;
+        }
+
+        int data = readBuffer[readPosition++];
+
+        if (readPosition >= SECTOR_SIZE) {
+            this.status = Status.IDLE;
+        }
+
+        return data;
+    }
+
+    private void writeData(int data) {
+        if (status != Status.WRITE) {
+            return;
+        }
+
+        writeBuffer[writePosition++] = (byte) data;
+
+        if (writePosition >= SECTOR_SIZE) {
+            if (sdImageFile != null) {
+                try {
+                    RandomAccessFile raf = new RandomAccessFile(sdImageFile, "rw");
+                    raf.skipBytes(this.position);
+                    raf.write(writeBuffer, 0, writeBuffer.length);
+                    raf.close();
+                } catch (IOException ex) {
+                    logger.log(Level.WARNING, "could not write data back to SD image file!", ex);
+                }
+            }
+
+            this.status = Status.IDLE;
+        }
+
+    }
+
+    private int readStatus() {
+        switch (this.status) {
+            case IDLE:
+                return 128;
+            case READ:
+                return 224;
+            case WRITE:
+                return 160;
+            default:
+                return 0;
+        }
+    }
+
+    private void writeCommand(int data) {
+        switch (data) {
+            case 0:
+                prepareRead();
+                return;
+            case 1:
+                prepareWrite();
+                return;
+            default:
+                this.status = Status.IDLE;
+        }
+    }
+
+    @Override
+    public String toString() {
+        return getName() + "@" + String.format("%04X", this.getMemoryRange().startAddress);
+    }
+
+}

src/main/java/com/loomcom/symon/devices/Via6522.java

@@ -0,0 +1,114 @@
+/*
+ * Copyright (c) 2008-2025 Seth J. Morabito <web@loomcom.com>
+ *
+ * Permission is hereby granted, free of charge, to any person obtaining
+ * a copy of this software and associated documentation files (the
+ * "Software"), to deal in the Software without restriction, including
+ * without limitation the rights to use, copy, modify, merge, publish,
+ * distribute, sublicense, and/or sell copies of the Software, and to
+ * permit persons to whom the Software is furnished to do so, subject to
+ * the following conditions:
+ *
+ * The above copyright notice and this permission notice shall be
+ * included in all copies or substantial portions of the Software.
+ *
+ * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND,
+ * EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF
+ * MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND
+ * NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS BE
+ * LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION
+ * OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION
+ * WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.
+ */
+
+package com.loomcom.symon.devices;
+
+import com.loomcom.symon.exceptions.MemoryAccessException;
+import com.loomcom.symon.exceptions.MemoryRangeException;
+import com.loomcom.symon.util.Utils;
+
+/**
+ * Skeleton for future implementation of a MOS 6522 VIA.
+ */
+public class Via6522 extends Pia {
+    public static final int VIA_SIZE = 16;
+
+
+    static final int IOB_REG    = 0;    // Output Register B / Input Register B
+    static final int IOA_REG    = 1;    // Output Register A / Input Register A
+    static final int DDRB_REG   = 2;    // Data Direction Register B
+    static final int DDRA_REG   = 3;    // Data Direction Register A
+    static final int T1CL_REG   = 4;    // T1 Low-Order Counter / Latches
+    static final int T1CH_REG   = 5;    // T1 High-Order Counter
+    static final int T1LL_REG   = 6;    // T1 Low-Order Latches
+    static final int T1LH_REG   = 7;    // T1 High-Order Latches
+    static final int T2CL_REG   = 8;    // T2 Low-Order Counter / Latches
+    static final int T2CH_REG   = 9;    // T2 High-Order Counter
+    static final int SR_REG     = 10;   // Shift Register
+    static final int AuxC_REG   = 11;   // Auxiliary Control Register
+    static final int PerC_REG   = 12;   // Peripheral Control Register
+    static final int IntF_REG   = 13;   // Interrupt Flag Register
+    static final int IntE_REG   = 14;   // Interrupt Enable Register
+    static final int IOANH_REG  = 15;   // Same as Register 1 (IOA), but no Handshake
+
+    private int outputRegisterB, inputRegisterB;
+    private int outputRegisterA, inputRegisterA;
+    private int dataDirectionB,  dataDirectionA;
+
+    public Via6522(int address) throws MemoryRangeException {
+        super(address, address + VIA_SIZE - 1, "MOS 6522 VIA");
+        outputRegisterA = outputRegisterB = 0;
+        dataDirectionA = dataDirectionB = 0;
+    }
+
+    @Override
+    public void write(int address, int data) throws MemoryAccessException {
+        switch (address) {
+            case IOB_REG    -> outputRegisterB  = data & 0xFF;
+            case IOA_REG    -> outputRegisterA  = data & 0xFF;
+            case DDRB_REG   -> dataDirectionB   = data & 0xFF;
+            case DDRA_REG   -> dataDirectionA   = data & 0xFF;
+            case IOANH_REG  -> outputRegisterA  = data & 0xFF;
+            default -> throw new MemoryAccessException("No Register or Not Implemented!");
+        }
+    }
+
+    @Override
+    public int read(int address, boolean cpuAccess) throws MemoryAccessException {
+        return switch (address) {
+            case IOB_REG    -> pbRead();
+            case IOA_REG    -> paRead();
+            case DDRB_REG   -> dataDirectionB;
+            case DDRA_REG   -> dataDirectionA;
+            case IOANH_REG  -> paRead();
+            default -> throw new MemoryAccessException("No Register or Not Implemented!");
+        };
+    }
+
+    public void setInputRegisterB(int data) {
+        inputRegisterB = data & 0xFF;
+    }
+
+    public void setInputRegisterA(int data) {
+        inputRegisterA = data & 0xFF;
+    }
+
+
+    public String getPBStatus() {
+        return "%" + Utils.byteToBin(pbRead());
+    }
+
+    public String getPAStatus() {
+        return "%" + Utils.byteToBin(paRead());
+    }
+
+    private int pbRead() {
+        // Return bits of output register where DDRB is 1 and input register where DDRB is 0
+        return (outputRegisterB & dataDirectionB) | (inputRegisterB & ~dataDirectionB);
+    }
+
+    private int paRead() {
+        // Return bits of output register where DDRB is 1 and input register where DDRB is 0
+        return (outputRegisterA & dataDirectionA) | (inputRegisterA & ~dataDirectionA);
+    }
+}

src/main/java/com/loomcom/symon/exceptions/FifoUnderrunException.java

@@ -1,5 +1,5 @@
 /*
- * Copyright (c) 2008-2013 Seth J. Morabito <sethm@loomcom.com>
+ * Copyright (c) 2008-2025 Seth J. Morabito <web@loomcom.com>
  *
  * Permission is hereby granted, free of charge, to any person obtaining
  * a copy of this software and associated documentation files (the

src/main/java/com/loomcom/symon/exceptions/MemoryAccessException.java

@@ -1,5 +1,5 @@
 /*
- * Copyright (c) 2008-2013 Seth J. Morabito <sethm@loomcom.com>
+ * Copyright (c) 2008-2025 Seth J. Morabito <web@loomcom.com>
  *
  * Permission is hereby granted, free of charge, to any person obtaining
  * a copy of this software and associated documentation files (the

src/main/java/com/loomcom/symon/exceptions/MemoryRangeException.java

@@ -1,5 +1,5 @@
 /*
- * Copyright (c) 2008-2013 Seth J. Morabito <sethm@loomcom.com>
+ * Copyright (c) 2008-2025 Seth J. Morabito <web@loomcom.com>
  *
  * Permission is hereby granted, free of charge, to any person obtaining
  * a copy of this software and associated documentation files (the

src/main/java/com/loomcom/symon/exceptions/SymonException.java

@@ -1,5 +1,5 @@
 /*
- * Copyright (c) 2008-2013 Seth J. Morabito <sethm@loomcom.com>
+ * Copyright (c) 2008-2025 Seth J. Morabito <web@loomcom.com>
  *
  * Permission is hereby granted, free of charge, to any person obtaining
  * a copy of this software and associated documentation files (the
@@ -31,7 +31,4 @@ public class SymonException extends Exception {
     public SymonException(String msg) {
         super(msg);
     }
-    public SymonException() {
-        super();
-    }
 }

src/main/java/com/loomcom/symon/jterminal/AbstractTerminalModel.java

@@ -0,0 +1,92 @@
+/*
+ * Copyright (c) 2009-2011 Graham Edgecombe.
+ *
+ * Permission is hereby granted, free of charge, to any person obtaining a copy
+ * of this software and associated documentation files (the "Software"), to
+ * deal in the Software without restriction, including without limitation the
+ * rights to use, copy, modify, merge, publish, distribute, sublicense, and/or
+ * sell copies of the Software, and to permit persons to whom the Software is
+ * furnished to do so, subject to the following conditions:
+ *
+ * The above copyright notice and this permission notice shall be included in
+ * all copies or substantial portions of the Software.
+ *
+ * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+ * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+ * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
+ * AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+ * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING
+ * FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER
+ * DEALINGS IN THE SOFTWARE.
+ */
+
+package com.loomcom.symon.jterminal;
+
+/**
+ * A {@link TerminalModel} which implements some common behaviour.
+ * @author Graham Edgecombe
+ */
+public abstract class AbstractTerminalModel implements TerminalModel {
+
+	@Override
+	public void clear() {
+		int rows = getRows(), columns = getColumns();
+		for (int column = 0; column < columns; column++) {
+			for (int row = 0; row < rows; row++) {
+				setCell(column, row, null);
+			}
+		}
+	}
+
+	@Override
+	public void moveCursorBack(int n) {
+		if (n < 0) {
+			throw new IllegalArgumentException("n must be positive");
+		}
+		int cursorColumn = getCursorColumn() - n;
+		if (cursorColumn < 0) {
+			cursorColumn = 0;
+		}
+		setCursorColumn(cursorColumn);
+	}
+
+	@Override
+	public void moveCursorForward(int n) {
+		if (n < 0) {
+			throw new IllegalArgumentException("n must be positive");
+		}
+		int columns = getColumns();
+		int cursorColumn = getCursorColumn() + n;
+		if (cursorColumn >= columns) {
+			cursorColumn = columns - 1;
+		}
+		setCursorColumn(cursorColumn);
+	}
+
+	@Override
+	public void moveCursorDown(int n) {
+		if (n < 0) {
+			throw new IllegalArgumentException("n must be positive");
+		}
+		int bufferSize = getBufferSize();
+		int cursorRow = getCursorRow() + n;
+		if (cursorRow >= bufferSize) {
+			cursorRow = bufferSize - 1;
+		}
+		setCursorRow(cursorRow);
+	}
+
+	@Override
+	public void moveCursorUp(int n) {
+		if (n < 0) {
+			throw new IllegalArgumentException("n must be positive");
+		}
+		int cursorRow = getCursorRow() - n;
+		if (cursorRow < 0) {
+			cursorRow = 0;
+		}
+		setCursorRow(cursorRow);
+	}
+
+}
+

src/main/java/com/loomcom/symon/jterminal/JTerminal.java

@@ -0,0 +1,178 @@
+/*
+ * Copyright (c) 2008-2025 Seth J. Morabito <web@loomcom.com>
+ * Portions Copyright (c) 2009-2011 Graham Edgecombe
+ *
+ * Permission is hereby granted, free of charge, to any person obtaining
+ * a copy of this software and associated documentation files (the
+ * "Software"), to deal in the Software without restriction, including
+ * without limitation the rights to use, copy, modify, merge, publish,
+ * distribute, sublicense, and/or sell copies of the Software, and to
+ * permit persons to whom the Software is furnished to do so, subject to
+ * the following conditions:
+ *
+ * The above copyright notice and this permission notice shall be
+ * included in all copies or substantial portions of the Software.
+ *
+ * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND,
+ * EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF
+ * MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND
+ * NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS BE
+ * LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION
+ * OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION
+ * WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.
+ */
+
+package com.loomcom.symon.jterminal;
+
+import com.loomcom.symon.jterminal.vt100.Vt100TerminalModel;
+
+import java.awt.*;
+import javax.swing.JComponent;
+import javax.swing.JScrollBar;
+
+/**
+ * Swing terminal emulation component
+ * @author Seth J. Morabito
+ *
+ */
+public class JTerminal extends JComponent {
+
+	private static final long serialVersionUID = 2871625194146986567L;
+
+	private int borderWidth = 0;
+
+	private JScrollBar scrollBar;
+
+	/**
+	 * The terminal emulation model
+	 */
+	private TerminalModel model;
+
+	/**
+	 * The font this terminal uses
+	 */
+	private Font font;
+
+	/**
+	 * The cell width in pixels
+	 */
+	private int cellWidth;
+
+	/**
+	 * The cell height in pixels
+	 */
+	private int cellHeight;
+
+	/**
+	 * Max descender for font 
+	 */
+	private int maxDescender;
+
+	public JTerminal(Font font) {
+		this(new Vt100TerminalModel(), font);
+	}
+
+	public JTerminal(TerminalModel model, Font font) {
+		setModel(model);
+		setFont(font);
+		init();
+	}
+
+	public void setBorderWidth(int borderWidth) {
+		this.borderWidth = borderWidth;
+		revalidate();
+	}
+
+	public void setFont(Font font) {
+		this.font = font;
+		setCellWidthAndHeight(font);
+		revalidate();
+	}
+
+	public Font getFont() {
+		return font;
+	}
+
+	public void setModel(TerminalModel model) {
+		if (model == null) {
+			throw new NullPointerException("model");
+		}
+		this.model = model;
+	}
+
+	public TerminalModel getModel() {
+		return model;
+	}
+
+	public void print(String str) {
+		model.print(str);
+	}
+
+	public Dimension getMinimumSize() {
+		return new Dimension(model.getColumns() * cellWidth + borderWidth * 2,
+				model.getRows() * cellHeight + borderWidth * 2);
+	}
+
+	public Dimension getMaximumSize() {
+		return getMinimumSize();
+	}
+
+	public Dimension getPreferredSize() {
+		return getMinimumSize();
+	}
+
+	public void paint(Graphics g) {
+		g.setFont(font);
+
+		int width = model.getColumns();
+		int height = model.getBufferSize();
+
+		g.setColor(model.getDefaultBackgroundColor());
+		g.fillRect(0, 0, width * cellWidth + borderWidth * 2, height * cellHeight + borderWidth * 2);
+
+		int start = scrollBar == null ? 0 : scrollBar.getValue();
+		for (int y = start; y < height; y++) {
+			for (int x = 0; x < width; x++) {
+				TerminalCell cell = model.getCell(x, y);
+				boolean cursorHere = (model.getCursorRow() == y) && (model.getCursorColumn() == x);
+
+				if ((cursorHere) && (cell == null)) {
+					cell = new TerminalCell(' ', model.getDefaultBackgroundColor(), model.getDefaultForegroundColor());
+				}
+
+				if (cell != null) {
+					int px = x * cellWidth + borderWidth;
+					int py = (y - start) * cellHeight + borderWidth;
+
+					g.setColor(cursorHere ? cell.getForegroundColor() : cell.getBackgroundColor());
+					g.fillRect(px, py, cellWidth, cellHeight);
+
+					g.setColor(cursorHere ? cell.getBackgroundColor() : cell.getForegroundColor());
+					g.drawChars(new char[] { cell.getCharacter() }, 0, 1, px, py + cellHeight - maxDescender);
+				}
+			}
+		}
+	}
+
+	private void init() {
+		setLayout(new BorderLayout(0, 0));
+
+		int rows = model.getRows();
+		int bufferSize = model.getBufferSize();
+
+		if (bufferSize > rows) {
+			scrollBar = new JScrollBar(Adjustable.VERTICAL, 0, rows, 0, bufferSize + 1);
+			scrollBar.addAdjustmentListener(evt -> repaint());
+			add("After", scrollBar);
+		}
+
+		repaint();
+	}
+
+	private void setCellWidthAndHeight(Font font) {
+		FontMetrics metrics = getFontMetrics(font);
+		cellWidth = metrics.charWidth('W');
+		cellHeight = metrics.getHeight();
+		maxDescender = metrics.getMaxDescent();
+	}
+}

src/main/java/com/loomcom/symon/jterminal/TerminalCell.java

@@ -0,0 +1,96 @@
+/*
+ * Copyright (c) 2009-2011 Graham Edgecombe.
+ *
+ * Permission is hereby granted, free of charge, to any person obtaining a copy
+ * of this software and associated documentation files (the "Software"), to
+ * deal in the Software without restriction, including without limitation the
+ * rights to use, copy, modify, merge, publish, distribute, sublicense, and/or
+ * sell copies of the Software, and to permit persons to whom the Software is
+ * furnished to do so, subject to the following conditions:
+ *
+ * The above copyright notice and this permission notice shall be included in
+ * all copies or substantial portions of the Software.
+ *
+ * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+ * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+ * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
+ * AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+ * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING
+ * FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER
+ * DEALINGS IN THE SOFTWARE.
+ */
+
+package com.loomcom.symon.jterminal;
+
+import java.awt.Color;
+
+/**
+ * Represents a single terminal cell which contains a character, background
+ * color and foreground color.
+ * @author Graham Edgecombe
+ */
+public class TerminalCell {
+
+	/**
+	 * The character.
+	 */
+	private final char character;
+
+	/**
+	 * The background color.
+	 */
+	private final Color backgroundColor;
+
+	/**
+	 * The foreground color.
+	 */
+	private final Color foregroundColor;
+
+	/**
+	 * Creates a terminal cell with the specified character, background color
+	 * and foreground color.
+	 * @param character The character.
+	 * @param backgroundColor The background color.
+	 * @param foregroundColor The foreground color.
+	 * @throws NullPointerException if the background or foreground color(s)
+	 * are {@code null}.
+	 */
+	public TerminalCell(char character, Color backgroundColor, Color foregroundColor) {
+		if (backgroundColor == null) {
+			throw new NullPointerException("backgroundColor");
+		}
+		if (foregroundColor == null) {
+			throw new NullPointerException("foregroundColor");
+		}
+
+		this.character = character;
+		this.backgroundColor = backgroundColor;
+		this.foregroundColor = foregroundColor;
+	}
+
+	/**
+	 * Gets the character.
+	 * @return The character.
+	 */
+	public char getCharacter() {
+		return character;
+	}
+
+	/**
+	 * Gets the background color.
+	 * @return The background color.
+	 */
+	public Color getBackgroundColor() {
+		return backgroundColor;
+	}
+
+	/**
+	 * Gets the foreground color.
+	 * @return The foreground color.
+	 */
+	public Color getForegroundColor() {
+		return foregroundColor;
+	}
+
+}
+

src/main/java/com/loomcom/symon/jterminal/TerminalModel.java

@@ -0,0 +1,161 @@
+/*
+ * Copyright (c) 2009-2011 Graham Edgecombe.
+ *
+ * Permission is hereby granted, free of charge, to any person obtaining a copy
+ * of this software and associated documentation files (the "Software"), to
+ * deal in the Software without restriction, including without limitation the
+ * rights to use, copy, modify, merge, publish, distribute, sublicense, and/or
+ * sell copies of the Software, and to permit persons to whom the Software is
+ * furnished to do so, subject to the following conditions:
+ *
+ * The above copyright notice and this permission notice shall be included in
+ * all copies or substantial portions of the Software.
+ *
+ * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+ * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+ * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
+ * AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+ * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING
+ * FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER
+ * DEALINGS IN THE SOFTWARE.
+ */
+
+package com.loomcom.symon.jterminal;
+
+import java.awt.Color;
+
+import com.loomcom.symon.jterminal.bell.BellStrategy;
+
+/**
+ * Model for terminals - defines methods for getting/setting cells, printing
+ * text to a terminal and getting the size of the terminal and buffer.
+ */
+public interface TerminalModel {
+
+	/**
+	 * Sets the bell strategy.
+	 * @param strategy The bell strategy.
+	 * @throws NullPointerException if the strategy is {@code null}.
+	 */
+    void setBellStrategy(BellStrategy strategy);
+
+	/**
+	 * Clears the terminal.
+	 */
+    void clear();
+
+	/**
+	 * Moves the cursor back n characters.
+	 * @param n The number of characters.
+	 * @throws IllegalArgumentException if n is not positive.
+	 */
+    void moveCursorBack(int n);
+
+	/**
+	 * Moves the cursor forward n characters.
+	 * @param n The number of characters.
+	 * @throws IllegalArgumentException if n is not positive.
+	 */
+    void moveCursorForward(int n);
+
+	/**
+	 * Moves the cursor down n characters.
+	 * @param n The number of characters.
+	 * @throws IllegalArgumentException if n is not positive.
+	 */
+    void moveCursorDown(int n);
+
+	/**
+	 * Moves the cursor up n characters.
+	 * @param n The number of characters.
+	 * @throws IllegalArgumentException if n is not positive.
+	 */
+    void moveCursorUp(int n);
+
+	/**
+	 * Sets a cell.
+	 * @param column The column.
+	 * @param row The row.
+	 * @param cell The cell.
+	 * @throws IndexOutOfBoundsException if the column and/or row number(s) are
+	 * out of bounds.
+	 */
+    void setCell(int column, int row, TerminalCell cell);
+
+	/**
+	 * Gets a cell.
+	 * @param column The column.
+	 * @param row The row.
+	 * @return The cell.
+	 * @throws IndexOutOfBoundsException if the column and/or row number(s) are
+	 * out of bounds.
+	 */
+    TerminalCell getCell(int column, int row);
+
+	/**
+	 * Prints the specified string to the terminal at the cursor position,
+	 * interpreting any escape sequences/special ASCII codes the model may
+	 * support. Lines will be wrapped if necessary.
+	 * @param str The string to print.
+	 * @throws NullPointerException if the string is {@code null}.
+	 */
+    void print(String str);
+
+	/**
+	 * Gets the number of columns.
+	 * @return The number of columns.
+	 */
+    int getColumns();
+
+	/**
+	 * Gets the number of rows.
+	 * @return The number of rows.
+	 */
+	int getRows();
+
+	/**
+	 * Gets the buffer size.
+	 * @return The buffer size.
+	 */
+	int getBufferSize();
+
+	/**
+	 * Gets the cursor row.
+	 * @return The cursor row.
+	 */
+	int getCursorRow();
+
+	/**
+	 * Sets the cursor row.
+	 * @param row The cursor row.
+	 * @throws IllegalArgumentException if the row is out of the valid range.
+	 */
+	void setCursorRow(int row);
+
+	/**
+	 * Gets the cursor column.
+	 * @return The cursor column.
+	 */
+	int getCursorColumn();
+
+	/**
+	 * Sets the cursor column.
+	 * @param column The cursor column.
+	 * @throws IllegalArgumentException if the column is out of the valid range.
+	 */
+	void setCursorColumn(int column);
+
+	/**
+	 * Gets the default background color.
+	 * @return The default background color.
+	 */
+	Color getDefaultBackgroundColor();
+
+	/**
+	 * Gets the default foreground color.
+	 * @return The default foreground color.
+	 */
+	Color getDefaultForegroundColor();
+
+}
+

src/main/java/com/loomcom/symon/jterminal/bell/BeepBellStrategy.java

@@ -0,0 +1,39 @@
+/*
+ * Copyright (c) 2009-2011 Graham Edgecombe.
+ *
+ * Permission is hereby granted, free of charge, to any person obtaining a copy
+ * of this software and associated documentation files (the "Software"), to
+ * deal in the Software without restriction, including without limitation the
+ * rights to use, copy, modify, merge, publish, distribute, sublicense, and/or
+ * sell copies of the Software, and to permit persons to whom the Software is
+ * furnished to do so, subject to the following conditions:
+ *
+ * The above copyright notice and this permission notice shall be included in
+ * all copies or substantial portions of the Software.
+ *
+ * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+ * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+ * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
+ * AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+ * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING
+ * FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER
+ * DEALINGS IN THE SOFTWARE.
+ */
+
+package com.loomcom.symon.jterminal.bell;
+
+import java.awt.Toolkit;
+
+/**
+ * A {@link BellStrategy} which calls {@link Toolkit#beep()}.
+ * @author Graham Edgecombe
+ */
+public class BeepBellStrategy implements BellStrategy {
+
+	@Override
+	public void soundBell() {
+		Toolkit.getDefaultToolkit().beep();
+	}
+
+}
+

src/main/java/com/loomcom/symon/jterminal/bell/BellStrategy.java

@@ -0,0 +1,37 @@
+/*
+ * Copyright (c) 2009-2011 Graham Edgecombe.
+ *
+ * Permission is hereby granted, free of charge, to any person obtaining a copy
+ * of this software and associated documentation files (the "Software"), to
+ * deal in the Software without restriction, including without limitation the
+ * rights to use, copy, modify, merge, publish, distribute, sublicense, and/or
+ * sell copies of the Software, and to permit persons to whom the Software is
+ * furnished to do so, subject to the following conditions:
+ *
+ * The above copyright notice and this permission notice shall be included in
+ * all copies or substantial portions of the Software.
+ *
+ * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+ * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+ * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
+ * AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+ * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING
+ * FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER
+ * DEALINGS IN THE SOFTWARE.
+ */
+
+package com.loomcom.symon.jterminal.bell;
+
+/**
+ * A 'strategy' used to sound the bell (US-ASCII character {@code 7}).
+ * @author Graham Edgecombe
+ */
+public interface BellStrategy {
+
+	/**
+	 * Sounds the bell.
+	 */
+	void soundBell();
+
+}
+

src/main/java/com/loomcom/symon/jterminal/bell/NopBellStrategy.java

@@ -0,0 +1,37 @@
+/*
+ * Copyright (c) 2009-2011 Graham Edgecombe.
+ *
+ * Permission is hereby granted, free of charge, to any person obtaining a copy
+ * of this software and associated documentation files (the "Software"), to
+ * deal in the Software without restriction, including without limitation the
+ * rights to use, copy, modify, merge, publish, distribute, sublicense, and/or
+ * sell copies of the Software, and to permit persons to whom the Software is
+ * furnished to do so, subject to the following conditions:
+ *
+ * The above copyright notice and this permission notice shall be included in
+ * all copies or substantial portions of the Software.
+ *
+ * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+ * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+ * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
+ * AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+ * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING
+ * FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER
+ * DEALINGS IN THE SOFTWARE.
+ */
+
+package com.loomcom.symon.jterminal.bell;
+
+/**
+ * A {@link BellStrategy} which does nothing.
+ * @author Graham Edgecombe
+ */
+public class NopBellStrategy implements BellStrategy {
+
+	@Override
+	public void soundBell() {
+		/* ignore */
+	}
+
+}
+

src/main/java/com/loomcom/symon/jterminal/vt100/AnsiControlSequence.java

@@ -0,0 +1,77 @@
+/*
+ * Copyright (c) 2009-2011 Graham Edgecombe.
+ *
+ * Permission is hereby granted, free of charge, to any person obtaining a copy
+ * of this software and associated documentation files (the "Software"), to
+ * deal in the Software without restriction, including without limitation the
+ * rights to use, copy, modify, merge, publish, distribute, sublicense, and/or
+ * sell copies of the Software, and to permit persons to whom the Software is
+ * furnished to do so, subject to the following conditions:
+ *
+ * The above copyright notice and this permission notice shall be included in
+ * all copies or substantial portions of the Software.
+ *
+ * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+ * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+ * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
+ * AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+ * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING
+ * FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER
+ * DEALINGS IN THE SOFTWARE.
+ */
+
+package com.loomcom.symon.jterminal.vt100;
+
+/**
+ * Represents an ANSI control sequence.
+ * @author Graham Edgecombe
+ */
+public class AnsiControlSequence {
+
+	/**
+	 * The command character.
+	 */
+	private final char command;
+
+	/**
+	 * The parameters.
+	 */
+	private final String[] parameters;
+
+	/**
+	 * Creates an ANSI control sequence with the specified command and
+	 * parameters.
+	 * @param command The command character.
+	 * @param parameters The parameters array.
+	 * @throws NullPointerException if the parameters array is {@code null}.
+	 */
+	public AnsiControlSequence(char command, String[] parameters) {
+		if (parameters == null) {
+			throw new NullPointerException("parameters");
+		}
+		this.command = command;
+		if (parameters.length == 1 && parameters[0].isEmpty()) {
+			this.parameters = new String[0];
+		} else {
+			this.parameters = parameters.clone();
+		}
+	}
+
+	/**
+	 * Gets the command character.
+	 * @return The command character.
+	 */
+	public char getCommand() {
+		return command;
+	}
+
+	/**
+	 * Gets the parameters array.
+	 * @return The parameters array.
+	 */
+	public String[] getParameters() {
+		return parameters;
+	}
+
+}
+

src/main/java/com/loomcom/symon/jterminal/vt100/AnsiControlSequenceListener.java

@@ -0,0 +1,44 @@
+/*
+ * Copyright (c) 2009-2011 Graham Edgecombe.
+ *
+ * Permission is hereby granted, free of charge, to any person obtaining a copy
+ * of this software and associated documentation files (the "Software"), to
+ * deal in the Software without restriction, including without limitation the
+ * rights to use, copy, modify, merge, publish, distribute, sublicense, and/or
+ * sell copies of the Software, and to permit persons to whom the Software is
+ * furnished to do so, subject to the following conditions:
+ *
+ * The above copyright notice and this permission notice shall be included in
+ * all copies or substantial portions of the Software.
+ *
+ * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+ * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+ * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
+ * AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+ * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING
+ * FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER
+ * DEALINGS IN THE SOFTWARE.
+ */
+
+package com.loomcom.symon.jterminal.vt100;
+
+/**
+ * An interface which classes may use to listen to events from a
+ * {@link AnsiControlSequenceParser}.
+ */
+public interface AnsiControlSequenceListener {
+
+	/**
+	 * Called when a control sequence has been parsed.
+	 * @param seq The control sequence.
+	 */
+	void parsedControlSequence(AnsiControlSequence seq);
+
+	/**
+	 * Called when a string has been parsed.
+	 * @param str The string.
+	 */
+	void parsedString(String str);
+
+}
+

src/main/java/com/loomcom/symon/jterminal/vt100/AnsiControlSequenceParser.java

@@ -0,0 +1,153 @@
+/*
+ * Copyright (c) 2009-2011 Graham Edgecombe.
+ *
+ * Permission is hereby granted, free of charge, to any person obtaining a copy
+ * of this software and associated documentation files (the "Software"), to
+ * deal in the Software without restriction, including without limitation the
+ * rights to use, copy, modify, merge, publish, distribute, sublicense, and/or
+ * sell copies of the Software, and to permit persons to whom the Software is
+ * furnished to do so, subject to the following conditions:
+ *
+ * The above copyright notice and this permission notice shall be included in
+ * all copies or substantial portions of the Software.
+ *
+ * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+ * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+ * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
+ * AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+ * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING
+ * FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER
+ * DEALINGS IN THE SOFTWARE.
+ */
+
+package com.loomcom.symon.jterminal.vt100;
+
+import java.io.IOException;
+import java.io.Reader;
+import java.io.StringReader;
+
+/**
+ * A class which parses {@link AnsiControlSequence}s from {@link String}(s).
+ * @author Graham Edgecombe
+ */
+public class AnsiControlSequenceParser {
+
+	/**
+	 * The multibyte control sequence introducer.
+	 */
+	private static final char[] MULTI_CSI = new char[] { 27, '[' };
+
+	/**
+	 * The single-byte control sequence introducer.
+	 */
+	private static final char SINGLE_CSI = 155;
+
+	/**
+	 * The buffer of data from the last call to "parse()". This is
+	 * populated with data if an escape sequence is not complete.
+	 */
+	private StringBuilder buffer = new StringBuilder();
+
+	/**
+	 * The ANSI control sequence listener.
+	 */
+	private final AnsiControlSequenceListener listener;
+
+	/**
+	 * Creates the ANSI control sequence parser.
+	 * @param listener The listener.
+	 */
+	public AnsiControlSequenceParser(AnsiControlSequenceListener listener) {
+		this.listener = listener;
+	}
+
+	/**
+	 * Parses the specified string.
+	 * @param str The string to parse.
+	 */
+	public void parse(String str) {
+		if (buffer.length() > 0) {
+			str = buffer.toString().concat(str);
+			buffer = new StringBuilder();
+		}
+        try {
+            try (Reader reader = new StringReader(str)) {
+                parse(reader);
+            }
+		} catch (IOException ex) {
+			/* ignore */
+		}
+	}
+
+	/**
+	 * Parses characters from the specified character reader.
+	 * @param reader The character reader.
+	 * @throws IOException if an I/O error occurs.
+	 */
+	private void parse(Reader reader) throws IOException {
+		StringBuilder text = new StringBuilder();
+		int character;
+		while ((character = reader.read()) != -1) {
+			boolean introducedControlSequence = false;
+			if (character == SINGLE_CSI) {
+				introducedControlSequence = true;
+			} else if (character == MULTI_CSI[0]) {
+				int nextCharacter = reader.read();
+				if (nextCharacter == -1) {
+					buffer.append((char) character);
+					break;
+				} else if (nextCharacter == MULTI_CSI[1]) {
+					introducedControlSequence = true;
+				} else {
+					text.append((char) character);
+					text.append((char) nextCharacter);
+				}
+			} else {
+				text.append((char) character);
+			}
+
+			if (introducedControlSequence) {
+				if (text.length() > 0) {
+					listener.parsedString(text.toString());
+					text = new StringBuilder();
+				}
+				parseControlSequence(reader);
+			}
+		}
+
+		if (text.length() > 0) {
+			listener.parsedString(text.toString());
+		}
+	}
+
+	/**
+	 * Parses a control sequence.
+	 * @param reader The character reader.
+	 * @throws IOException if an I/O error occurs.
+	 */
+	private void parseControlSequence(Reader reader) throws IOException {
+		boolean finishedSequence = false;
+		StringBuilder parameters = new StringBuilder();
+		int character;
+		while ((character = reader.read()) != -1) {
+			if ((character >= 'a' && character <= 'z') || (character >= 'A' && character <= 'Z')) {
+				String[] array = parameters.toString().split(";");
+				AnsiControlSequence seq = new AnsiControlSequence((char) character, array);
+				listener.parsedControlSequence(seq);
+
+				finishedSequence = true;
+				break;
+			} else {
+				parameters.append((char) character);
+			}
+		}
+		if (!finishedSequence) {
+			// not an ideal solution if they used the two byte CSI, but it's
+			// easier and cleaner than keeping track of it
+			buffer.append(SINGLE_CSI);
+			buffer.append(parameters);
+		}
+	}
+
+}
+

src/main/java/com/loomcom/symon/jterminal/vt100/SgrColor.java

@@ -0,0 +1,70 @@
+/*
+ * Copyright (c) 2009-2011 Graham Edgecombe.
+ *
+ * Permission is hereby granted, free of charge, to any person obtaining a copy
+ * of this software and associated documentation files (the "Software"), to
+ * deal in the Software without restriction, including without limitation the
+ * rights to use, copy, modify, merge, publish, distribute, sublicense, and/or
+ * sell copies of the Software, and to permit persons to whom the Software is
+ * furnished to do so, subject to the following conditions:
+ *
+ * The above copyright notice and this permission notice shall be included in
+ * all copies or substantial portions of the Software.
+ *
+ * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+ * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+ * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
+ * AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+ * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING
+ * FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER
+ * DEALINGS IN THE SOFTWARE.
+ */
+
+package com.loomcom.symon.jterminal.vt100;
+
+import java.awt.Color;
+
+/**
+ * Contains colors used by the SGR ANSI escape sequence.
+ * @author Graham Edgecombe
+ */
+final class SgrColor {
+
+	/**
+	 * An array of normal intensity colors.
+	 */
+	public static final Color[] COLOR_NORMAL = new Color[] {
+		new Color(0, 0, 0),
+		new Color(128, 0, 0),
+		new Color(0, 128, 0),
+		new Color(128, 128, 0),
+		new Color(0, 0, 128),
+		new Color(128, 0, 128),
+		new Color(0, 128, 128),
+		new Color(192, 192, 192)
+	};
+
+	/**
+	 * An array of bright intensity colors.
+	 */
+	public static final Color[] COLOR_BRIGHT = new Color[] {
+		new Color(128, 128, 128),
+		new Color(255, 0, 0),
+		new Color(0, 255, 0),
+		new Color(255, 255, 0),
+		new Color(0, 0, 255),
+		new Color(0, 0, 255),
+		new Color(255, 0, 255),
+		new Color(0, 255, 255),
+		new Color(255, 255, 255)
+	};
+
+	/**
+	 * Default private constructor to prevent instantiation.
+	 */
+	private SgrColor() {
+
+	}
+
+}
+

src/main/java/com/loomcom/symon/jterminal/vt100/Vt100TerminalModel.java

@@ -0,0 +1,490 @@
+/*
+ * Copyright (c) 2009-2011 Graham Edgecombe.
+ *
+ * Permission is hereby granted, free of charge, to any person obtaining a copy
+ * of this software and associated documentation files (the "Software"), to
+ * deal in the Software without restriction, including without limitation the
+ * rights to use, copy, modify, merge, publish, distribute, sublicense, and/or
+ * sell copies of the Software, and to permit persons to whom the Software is
+ * furnished to do so, subject to the following conditions:
+ *
+ * The above copyright notice and this permission notice shall be included in
+ * all copies or substantial portions of the Software.
+ *
+ * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+ * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+ * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
+ * AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+ * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING
+ * FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER
+ * DEALINGS IN THE SOFTWARE.
+ */
+
+package com.loomcom.symon.jterminal.vt100;
+
+import java.awt.Color;
+
+import com.loomcom.symon.jterminal.AbstractTerminalModel;
+import com.loomcom.symon.jterminal.TerminalCell;
+import com.loomcom.symon.jterminal.TerminalModel;
+import com.loomcom.symon.jterminal.bell.BellStrategy;
+import com.loomcom.symon.jterminal.bell.NopBellStrategy;
+
+/**
+ * A VT100/ANSI-compatible terminal model.
+ * @author Graham Edgecombe
+ */
+public class Vt100TerminalModel extends AbstractTerminalModel {
+
+	/**
+	 * A {@link AnsiControlSequenceListener} which modifies the
+	 * {@link TerminalModel} appropriately when an event happens.
+	 * @author Graham Edgecombe
+	 */
+	private class Vt100Listener implements AnsiControlSequenceListener {
+
+		/**
+		 * The saved cursor row.
+		 */
+		private int savedCursorRow = -1;
+
+		/**
+		 * The saved cursor column.
+		 */
+		private int savedCursorColumn = -1;
+
+		@Override
+		public void parsedControlSequence(AnsiControlSequence seq) {
+			char command = seq.getCommand();
+			int n;
+			String[] parameters = seq.getParameters();
+
+			switch (command) {
+			case 'A':
+			case 'B':
+			case 'C':
+			case 'D':
+				n = 1;
+				if (parameters.length == 1) {
+					n = Integer.parseInt(parameters[0]);
+				}
+				if (command == 'A') {
+					moveCursorUp(n);
+				} else if (command == 'B') {
+					moveCursorDown(n);
+				} else if (command == 'C') {
+					moveCursorForward(n);
+				} else {
+					moveCursorBack(n);
+				}
+				break;
+			case 'E':
+			case 'F':
+				n = 1;
+				if (parameters.length == 1) {
+					n = Integer.parseInt(parameters[0]);
+				}
+				if (command == 'E') {
+					moveCursorDown(n);
+				} else {
+					moveCursorUp(n);
+				}
+				setCursorColumn(0);
+				break;
+			case 'G':
+				if (parameters.length == 1) {
+					n = Integer.parseInt(parameters[0]);
+					setCursorColumn(n - 1);
+				}
+				break;
+			case 'H':
+			case 'f':
+				if (parameters.length == 2) {
+					n = 1;
+					int m = 1;
+					if (parameters[0].length() > 0) {
+						n = Integer.parseInt(parameters[0]);
+					}
+					if (parameters[1].length() > 0) {
+						m = Integer.parseInt(parameters[1]);
+					}
+					setCursorRow(n - 1);
+					setCursorColumn(m - 1);
+				}
+				break;
+			case 'J':
+				n = 0;
+				if (parameters.length == 1) {
+					n = Integer.parseInt(parameters[0]);
+				}
+				if (n == 0) {
+					int row = cursorRow;
+					int column = cursorColumn;
+					while(row < rows) {
+						while(column < columns) {
+							cells[row][column] = null;
+							column++;
+						}
+						column = 0;
+						row++;
+					}
+				} else if (n == 1) {
+					int row = cursorRow;
+					int column = cursorColumn;
+					while(row >= 0) {
+						while(column >= 0) {
+							cells[row][column] = null;
+							column--;
+						}
+						column = columns - 1;
+						row--;
+					}
+				} else if (n == 2) {
+					clear();
+				}
+				break;
+			case 'K':
+				n = 0;
+				if (parameters.length == 1) {
+					n = Integer.parseInt(parameters[0]);
+				}
+				if (n == 0) {
+					for (int row = cursorRow; row < rows; row++) {
+						cells[row][cursorColumn] = null;
+					}
+				} else if (n == 1) {
+					for (int row = cursorRow; row >= 0; row--) {
+						cells[row][cursorColumn] = null;
+					}
+				} else if (n == 2) {
+					for (int column = 0; column < columns; column++) {
+						cells[cursorRow][column] = null;
+					}
+				}
+				break;
+			case 'm':
+				if (parameters.length == 0) {
+					parameters = new String[] { "0" };
+				}
+				for (String parameter : parameters) {
+					if (parameter.equals("0")) {
+						foregroundColor = DEFAULT_FOREGROUND_COLOR;
+						backgroundColor = DEFAULT_BACKGROUND_COLOR;
+						backgroundBold = DEFAULT_BACKGROUND_BOLD;
+						foregroundBold = DEFAULT_FOREGROUND_BOLD;
+					} else if (parameter.equals("2")) {
+						backgroundBold = true;
+						foregroundBold = true;
+					} else if (parameter.equals("22")) {
+						backgroundBold = false;
+						foregroundBold = false;
+					} else if ((parameter.startsWith("3") || parameter.startsWith("4")) && parameter.length() == 2) {
+						int color = Integer.parseInt(parameter.substring(1));
+						if (parameter.startsWith("3")) {
+							foregroundColor = color;
+						} else if (parameter.startsWith("4")) {
+							backgroundColor = color;
+						}
+					}
+				}
+				break;
+			case 'u':
+				if (savedCursorColumn != -1 && savedCursorRow != -1) {
+					cursorColumn = savedCursorColumn;
+					cursorRow = savedCursorRow;
+				}
+				break;
+			case 's':
+				savedCursorColumn = cursorColumn;
+				savedCursorRow = cursorRow;
+				break;
+			}
+		}
+
+		@Override
+		public void parsedString(String str) {
+			for (char ch : str.toCharArray()) {
+				switch (ch) {
+				case '\0':
+					continue;
+				case '\r':
+					cursorColumn = 0;
+					continue;
+				case '\n':
+					cursorRow++;
+					break;
+				case '\t':
+					while ((++cursorColumn % TAB_WIDTH) != 0);
+					continue;
+				case 8:   // ASCII Backspace
+				case 127: // ASCII Delete
+					if (cursorColumn > 0) {
+						cells[cursorRow][--cursorColumn] = null;
+					}
+					continue;
+				case 7:
+					bellStrategy.soundBell();
+					continue;
+				}
+
+				if (cursorColumn >= columns) {
+					cursorColumn = 0;
+					cursorRow++;
+				}
+
+				if (cursorRow >= bufferSize) {
+					for (int i = 1; i < bufferSize; i++) {
+						System.arraycopy(cells[i], 0, cells[i - 1], 0, columns);
+					}
+					for (int i = 0; i < columns; i++) {
+						cells[bufferSize - 1][i] = null;
+					}
+					cursorRow--;
+				}
+
+				Color back = backgroundBold ? SgrColor.COLOR_BRIGHT[backgroundColor] : SgrColor.COLOR_NORMAL[backgroundColor];
+				Color fore = foregroundBold ? SgrColor.COLOR_BRIGHT[foregroundColor] : SgrColor.COLOR_NORMAL[foregroundColor];
+				if (ch != '\n') {
+					cells[cursorRow][cursorColumn++] = new TerminalCell(ch, back, fore);
+				}
+			}
+		}
+
+	}
+
+	/**
+	 * The default number of columns.
+	 */
+	private static final int DEFAULT_COLUMNS = 80;
+
+	/**
+	 * The default number of rows.
+	 */
+	private static final int DEFAULT_ROWS = 25;
+
+	/**
+	 * The tab width in characters.
+	 */
+	private static final int TAB_WIDTH = 8;
+
+	/**
+	 * The default foreground bold flag.
+	 */
+	private static final boolean DEFAULT_FOREGROUND_BOLD = false;
+
+	/**
+	 * The default background bold flag.
+	 */
+	private static final boolean DEFAULT_BACKGROUND_BOLD = false;
+
+	/**
+	 * The default foreground color.
+	 */
+	private static final int DEFAULT_FOREGROUND_COLOR = 7;
+
+	/**
+	 * The default background color.
+	 */
+	private static final int DEFAULT_BACKGROUND_COLOR = 0;
+
+	/**
+	 * The ANSI control sequence listener.
+	 */
+	private final AnsiControlSequenceListener listener = this.new Vt100Listener();
+
+	/**
+	 * The ANSI control sequence parser.
+	 */
+	private final AnsiControlSequenceParser parser = new AnsiControlSequenceParser(listener);
+
+	/**
+	 * The current bell strategy.
+	 */
+	private BellStrategy bellStrategy = new NopBellStrategy();
+
+	/**
+	 * The array of cells.
+	 */
+	private TerminalCell[][] cells;
+
+	/**
+	 * The number of columns.
+	 */
+	private int columns;
+
+	/**
+	 * The number of rows.
+	 */
+	private int rows;
+
+	/**
+	 * The buffer size.
+	 */
+	private int bufferSize;
+
+	/**
+	 * The cursor row.
+	 */
+	private int cursorRow = 0;
+
+	/**
+	 * The cursor column.
+	 */
+	private int cursorColumn = 0;
+
+	/**
+	 * The current foreground bold flag.
+	 */
+	private boolean foregroundBold = DEFAULT_FOREGROUND_BOLD;
+
+	/**
+	 * The current background bold flag.
+	 */
+	private boolean backgroundBold = DEFAULT_BACKGROUND_BOLD;
+
+	/**
+	 * The current foreground color.
+	 */
+	private int foregroundColor = DEFAULT_FOREGROUND_COLOR;
+
+	/**
+	 * The current background color.
+	 */
+	private int backgroundColor = DEFAULT_BACKGROUND_COLOR;
+
+	/**
+	 * Creates the terminal model with the default number of columns and rows,
+	 * and the default buffer size.
+	 */
+	public Vt100TerminalModel() {
+		this(DEFAULT_COLUMNS, DEFAULT_ROWS);
+	}
+
+	/**
+	 * Creates the terminal model with the specified number of columns and
+	 * rows. The buffer size is set to the number of rows.
+	 * @param columns The number of columns.
+	 * @param rows The number of rows.
+	 * @throws IllegalArgumentException if the number of rows or columns is
+	 * negative.
+	 */
+	public Vt100TerminalModel(int columns, int rows) {
+		this(columns, rows, rows);
+	}
+
+	/**
+	 * Creates the terminal model with the specified number of columns and rows
+	 * and the specified buffer size.
+	 * @param columns The number of columns.
+	 * @param rows The number of rows.
+	 * @param bufferSize The buffer size.
+	 * @throws IllegalArgumentException if the number of rows or columns is
+	 * negative, or if the buffer size is less than the number of rows.
+	 */
+	public Vt100TerminalModel(int columns, int rows, int bufferSize) {
+		if (columns < 0 || rows < 0 || bufferSize < 0) {
+			throw new IllegalArgumentException("Zero or positive values only allowed for columns, rows and buffer size.");
+		}
+		if (bufferSize < rows) {
+			throw new IllegalArgumentException("The buffer is too small");
+		}
+		this.columns = columns;
+		this.rows = rows;
+		this.bufferSize = bufferSize;
+		init();
+	}
+
+	/**
+	 * Initializes the terminal model.
+	 */
+	private void init() {
+		cells = new TerminalCell[bufferSize][columns];
+	}
+
+	@Override
+	public int getCursorRow() {
+		return cursorRow;
+	}
+
+	@Override
+	public void setCursorRow(int row) {
+		if (row < 0 || row >= bufferSize) {
+			throw new IllegalArgumentException("row out of range");
+		}
+		cursorRow = row;
+	}
+
+	@Override
+	public int getCursorColumn() {
+		return cursorColumn;
+	}
+
+	@Override
+	public void setCursorColumn(int column) {
+		if (column < 0 || column >= columns) {
+			throw new IllegalArgumentException("column out of range");
+		}
+		cursorColumn = column;
+	}
+
+	@Override
+	public TerminalCell getCell(int column, int row) {
+		if (column < 0 || row < 0 || column >= columns || row >= bufferSize) {
+			throw new IndexOutOfBoundsException();
+		}
+		return cells[row][column];
+	}
+
+	@Override
+	public void setCell(int column, int row, TerminalCell cell) {
+		if (column < 0 || row < 0 || column >= columns || row >= bufferSize) {
+			throw new IndexOutOfBoundsException();
+		}
+		cells[row][column] = cell;
+	}
+
+	@Override
+	public void print(String str) {
+		if (str == null) {
+			throw new NullPointerException("str");
+		}
+		parser.parse(str);
+	}
+
+	@Override
+	public int getColumns() {
+		return columns;
+	}
+
+	@Override
+	public int getRows() {
+		return rows;
+	}
+
+	@Override
+	public int getBufferSize() {
+		return bufferSize;
+	}
+
+    @Override
+	public void setBellStrategy(BellStrategy strategy) {
+		if (strategy == null) {
+			throw new NullPointerException("strategy");
+		}
+		this.bellStrategy = strategy;
+	}
+
+	@Override
+	public Color getDefaultBackgroundColor() {
+		final int bg = DEFAULT_BACKGROUND_COLOR;
+		return DEFAULT_BACKGROUND_BOLD ? SgrColor.COLOR_BRIGHT[bg] : SgrColor.COLOR_NORMAL[bg];
+	}
+
+	@Override
+	public Color getDefaultForegroundColor() {
+		final int fg = DEFAULT_FOREGROUND_COLOR;
+		return DEFAULT_FOREGROUND_BOLD ? SgrColor.COLOR_BRIGHT[fg] : SgrColor.COLOR_NORMAL[fg];
+	}
+
+}
+

src/main/java/com/loomcom/symon/machines/BenEaterMachine.java

@@ -0,0 +1,169 @@
+/*
+ * Copyright (c) 2008-2025 Seth J. Morabito <web@loomcom.com>
+ *                         Maik Merten <maikmerten@googlemail.com>
+ *                         Chelsea Wilkinson <mail@chelseawilkinson.me>
+ *
+ * Permission is hereby granted, free of charge, to any person obtaining
+ * a copy of this software and associated documentation files (the
+ * "Software"), to deal in the Software without restriction, including
+ * without limitation the rights to use, copy, modify, merge, publish,
+ * distribute, sublicense, and/or sell copies of the Software, and to
+ * permit persons to whom the Software is furnished to do so, subject to
+ * the following conditions:
+ *
+ * The above copyright notice and this permission notice shall be
+ * included in all copies or substantial portions of the Software.
+ *
+ * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND,
+ * EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF
+ * MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND
+ * NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS BE
+ * LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION
+ * OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION
+ * WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.
+ */
+
+package com.loomcom.symon.machines;
+
+import com.loomcom.symon.Bus;
+import com.loomcom.symon.Cpu;
+import com.loomcom.symon.devices.*;
+import com.loomcom.symon.exceptions.MemoryRangeException;
+import org.slf4j.Logger;
+import org.slf4j.LoggerFactory;
+
+import java.io.File;
+
+public class BenEaterMachine implements Machine {
+
+    private final static Logger logger = LoggerFactory.getLogger(BenEaterMachine.class.getName());
+
+    // Constants used by the simulated system. These define the memory map.
+    private static final int BUS_BOTTOM = 0x0000;
+    private static final int BUS_TOP    = 0xffff;
+
+    // 16K of RAM from $0000 - $3FFF
+    private static final int MEMORY_BASE = 0x0000;
+    private static final int MEMORY_SIZE = 0x4000;
+
+    // VIA at $6000-$600F
+    private static final int PIA_BASE = 0x6000;
+
+    // ACIA at $5000-$5003
+    private static final int ACIA_BASE = 0x5000;
+
+    // CRTC at $4000-$4001
+    private static final int CRTC_BASE = 0x4000;
+
+    // 32KB ROM at $8000-$FFFF
+    private static final int ROM_BASE = 0x8000;
+    private static final int ROM_SIZE = 0x8000;
+
+
+        // The simulated peripherals
+    private final Bus    bus;
+    private final Cpu    cpu;
+    private final Acia   acia;
+    private final Pia    pia;
+    private final Crtc   crtc;
+    private final Memory ram;
+    private       Memory rom;
+
+
+    public BenEaterMachine(String romFile) throws Exception {
+        this.bus = new Bus(BUS_BOTTOM, BUS_TOP);
+        this.cpu = new Cpu();
+        this.ram = new Memory(MEMORY_BASE, MEMORY_BASE + MEMORY_SIZE - 1, false);
+        this.pia = new Via6522(PIA_BASE);
+        this.acia = new Acia6551(ACIA_BASE);
+        this.crtc = new Crtc(CRTC_BASE, ram);
+
+        bus.addCpu(cpu);
+        bus.addDevice(ram);
+        bus.addDevice(pia);
+        bus.addDevice(acia);
+        bus.addDevice(crtc);
+
+        if (romFile != null) {
+            File romImage = new File(romFile);
+            if (romImage.canRead()) {
+                logger.info("Loading ROM image from file {}", romImage);
+                this.rom = Memory.makeROM(ROM_BASE, ROM_BASE + ROM_SIZE - 1, romImage);
+            } else {
+                logger.info("Default ROM file {} not found, loading empty R/W memory image.", romImage);
+                this.rom = Memory.makeRAM(ROM_BASE, ROM_BASE + ROM_SIZE - 1);
+            }
+        } else {
+            logger.info("No ROM file specified, loading empty R/W memory image.");
+            this.rom = Memory.makeRAM(ROM_BASE, ROM_BASE + ROM_SIZE - 1);
+        }
+
+        bus.addDevice(rom);
+
+    }
+
+    @Override
+    public Bus getBus() {
+        return bus;
+    }
+
+    @Override
+    public Cpu getCpu() {
+        return cpu;
+    }
+
+    @Override
+    public Memory getRam() {
+        return ram;
+    }
+
+    @Override
+    public Acia getAcia() {
+        return acia;
+    }
+
+    @Override
+    public Pia getPia() {
+        return pia;
+    }
+
+    @Override
+    public Crtc getCrtc() {
+        return crtc;
+    }
+
+    @Override
+    public Memory getRom() {
+        return rom;
+    }
+
+    public void setRom(Memory rom) throws MemoryRangeException {
+        if(this.rom != null) {
+            bus.removeDevice(this.rom);
+        }
+        this.rom = rom;
+        bus.addDevice(this.rom);
+    }
+
+    @Override
+    public int getRomBase() {
+        return ROM_BASE;
+    }
+
+    @Override
+    public int getRomSize() {
+        return ROM_SIZE;
+    }
+
+    @Override
+    public int getMemorySize() {
+        return MEMORY_SIZE;
+    }
+
+    @Override
+    public String getName() {
+        return "benEater";
+    }
+
+
+}

src/main/java/com/loomcom/symon/machines/Machine.java

@@ -0,0 +1,61 @@
+/*
+ * Copyright (c) 2008-2025 Seth J. Morabito <web@loomcom.com>
+ *                         Maik Merten <maikmerten@googlemail.com>
+ *
+ * Permission is hereby granted, free of charge, to any person obtaining
+ * a copy of this software and associated documentation files (the
+ * "Software"), to deal in the Software without restriction, including
+ * without limitation the rights to use, copy, modify, merge, publish,
+ * distribute, sublicense, and/or sell copies of the Software, and to
+ * permit persons to whom the Software is furnished to do so, subject to
+ * the following conditions:
+ *
+ * The above copyright notice and this permission notice shall be
+ * included in all copies or substantial portions of the Software.
+ *
+ * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND,
+ * EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF
+ * MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND
+ * NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS BE
+ * LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION
+ * OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION
+ * WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.
+ */
+
+package com.loomcom.symon.machines;
+
+import com.loomcom.symon.Bus;
+import com.loomcom.symon.Cpu;
+import com.loomcom.symon.devices.Acia;
+import com.loomcom.symon.devices.Crtc;
+import com.loomcom.symon.devices.Memory;
+import com.loomcom.symon.devices.Pia;
+import com.loomcom.symon.exceptions.MemoryRangeException;
+
+
+public interface Machine {
+    
+    Bus getBus();
+
+    Cpu getCpu();
+    
+    Memory getRam();
+    
+    Acia getAcia();
+
+    Pia getPia();
+
+    Crtc getCrtc();
+    
+    Memory getRom();
+    
+    void setRom(Memory rom) throws MemoryRangeException;
+    
+    int getRomBase();
+    
+    int getRomSize();
+    
+    int getMemorySize();
+
+    String getName();
+}

src/main/java/com/loomcom/symon/machines/MichaelBillingtonMachine.java

@@ -0,0 +1,133 @@
+package com.loomcom.symon.machines;
+
+import com.loomcom.symon.Bus;
+import com.loomcom.symon.Cpu;
+import com.loomcom.symon.devices.*;
+import com.loomcom.symon.exceptions.MemoryRangeException;
+import org.slf4j.Logger;
+import org.slf4j.LoggerFactory;
+
+import java.io.File;
+
+public class MichaelBillingtonMachine implements Machine{
+
+    private static final Logger logger = LoggerFactory.getLogger(MichaelBillingtonMachine.class.getName());
+
+    // Constants used by the simulated system
+    private static final int BUS_BOTTOM = 0x0000;
+    private static final int BUS_TOP    = 0xffff;
+
+    // 32k of ram, from $0000 to $7fff
+    private static final int MEMORY_BASE = 0x0000;
+    private static final int MEMORY_SIZE = 0x8000;
+
+    // VIA at $8000-$800f
+    private static final int PIA_BASE = 0x8000;
+
+    // ACIA at $8400-$8403
+    private static final int ACIA_BASE = 0x8400;
+
+    // 16k ROM from $c000 to $ffff
+    private static final int ROM_BASE = 0xc000;
+    private static final int ROM_SIZE = 0x4000;
+
+    private final   Bus     bus;
+    private final   Cpu     cpu;
+    private final   Acia    acia;
+    private final   Pia     pia;
+    private final   Memory  ram;
+    private         Memory  rom;
+
+    public MichaelBillingtonMachine(String romFile) throws Exception {
+        this.bus = new Bus(BUS_BOTTOM, BUS_TOP);
+        this.cpu = new Cpu();
+        this.ram = new Memory(MEMORY_BASE, MEMORY_BASE + MEMORY_SIZE - 1);
+        this.pia = new Via6522(PIA_BASE);
+        this.acia = new Acia6551(ACIA_BASE);
+
+        bus.addCpu(cpu);
+        bus.addDevice(ram);
+        bus.addDevice(pia);
+        bus.addDevice(acia);
+
+        if (romFile != null) {
+            File romImage = new File(romFile);
+            if (romImage.canRead()) {
+                logger.info("Loading ROM image from file {}", romImage);
+                this.rom = Memory.makeROM(ROM_BASE, ROM_BASE + ROM_SIZE - 1, romImage);
+            } else {
+                logger.info("Default ROM file {} not found, loading empty R/W memory image.", romImage);
+                this.rom = Memory.makeRAM(ROM_BASE, ROM_BASE + ROM_SIZE - 1);
+            }
+        } else {
+            logger.info("No ROM file specified, loading empty R/W memory image.");
+            this.rom = Memory.makeRAM(ROM_BASE, ROM_BASE + ROM_SIZE - 1);
+        }
+
+        bus.addDevice(rom);
+    }
+
+    @Override
+    public Bus getBus() {
+        return bus;
+    }
+
+    @Override
+    public Cpu getCpu() {
+        return cpu;
+    }
+
+    @Override
+    public Memory getRam() {
+        return ram;
+    }
+
+    @Override
+    public Acia getAcia() {
+        return acia;
+    }
+
+    @Override
+    public Pia getPia() {
+        return pia;
+    }
+
+    @Override
+    public Crtc getCrtc() {
+        return null;
+    }
+
+    @Override
+    public Memory getRom() {
+        return rom;
+    }
+
+    @Override
+    public void setRom(Memory rom) throws MemoryRangeException {
+        if (this.rom != null) {
+            bus.removeDevice(this.rom);
+        }
+        this.rom = rom;
+        bus.addDevice(this.rom);
+    }
+
+    @Override
+    public int getRomBase() {
+        return ROM_BASE;
+    }
+
+    @Override
+    public int getRomSize() {
+        return ROM_SIZE;
+    }
+
+    @Override
+    public int getMemorySize() {
+        return MEMORY_SIZE;
+    }
+
+    @Override
+    public String getName() {
+        return "mike42";
+    }
+}

src/main/java/com/loomcom/symon/machines/MulticompMachine.java

@@ -0,0 +1,164 @@
+/*
+ * Copyright (c) 2008-2025 Seth J. Morabito <web@loomcom.com>
+ *                         Maik Merten <maikmerten@googlemail.com>
+ *
+ * Permission is hereby granted, free of charge, to any person obtaining
+ * a copy of this software and associated documentation files (the
+ * "Software"), to deal in the Software without restriction, including
+ * without limitation the rights to use, copy, modify, merge, publish,
+ * distribute, sublicense, and/or sell copies of the Software, and to
+ * permit persons to whom the Software is furnished to do so, subject to
+ * the following conditions:
+ *
+ * The above copyright notice and this permission notice shall be
+ * included in all copies or substantial portions of the Software.
+ *
+ * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND,
+ * EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF
+ * MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND
+ * NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS BE
+ * LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION
+ * OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION
+ * WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.
+ */
+
+package com.loomcom.symon.machines;
+
+import com.loomcom.symon.Bus;
+import com.loomcom.symon.Cpu;
+import com.loomcom.symon.devices.Acia;
+import com.loomcom.symon.devices.Acia6850;
+import com.loomcom.symon.devices.Crtc;
+import com.loomcom.symon.devices.Memory;
+import com.loomcom.symon.devices.Pia;
+import com.loomcom.symon.devices.SdController;
+import com.loomcom.symon.exceptions.MemoryRangeException;
+import java.io.File;
+import java.util.logging.Logger;
+
+
+public class MulticompMachine implements Machine {
+    
+    private final static Logger logger = Logger.getLogger(MulticompMachine.class.getName());
+    
+    // Constants used by the simulated system. These define the memory map.
+    private static final int BUS_BOTTOM = 0x0000;
+    private static final int BUS_TOP    = 0xffff;
+
+    // 56K of RAM from $0000 - $DFFF
+    private static final int MEMORY_BASE = 0x0000;
+    private static final int MEMORY_SIZE = 0xE000;
+
+    // ACIA at $FFD0-$FFD1
+    private static final int ACIA_BASE = 0xFFD0;
+
+    // SD controller at $FFD8-$FFDF
+    private static final int SD_BASE = 0xFFD8;
+
+    // 8KB ROM at $E000-$FFFF
+    private static final int ROM_BASE = 0xE000;
+    private static final int ROM_SIZE = 0x2000;
+
+
+        // The simulated peripherals
+    private final Bus    bus;
+    private final Cpu    cpu;
+    private final Acia   acia;
+    private final Memory ram;
+    private       Memory rom;
+
+
+    public MulticompMachine(String romFile) throws Exception {
+        this.bus = new Bus(BUS_BOTTOM, BUS_TOP);
+        this.cpu = new Cpu();
+        this.ram = new Memory(MEMORY_BASE, MEMORY_BASE + MEMORY_SIZE - 1, false);
+        this.acia = new Acia6850(ACIA_BASE);
+        this.acia.setBaudRate(0);
+
+        bus.addCpu(cpu);
+        bus.addDevice(ram);
+        bus.addDevice(acia, 1);
+        bus.addDevice(new SdController(SD_BASE), 1);
+
+        if (romFile != null) {
+            File romImage = new File("rom.bin");
+            if (romImage.canRead()) {
+                logger.info("Loading ROM image from file " + romImage);
+                this.rom = Memory.makeROM(ROM_BASE, ROM_BASE + ROM_SIZE - 1, romImage);
+            } else {
+                logger.info("Default ROM file " + romImage +
+                        " not found, loading empty R/W memory image.");
+                this.rom = Memory.makeRAM(ROM_BASE, ROM_BASE + ROM_SIZE - 1);
+            }
+        } else {
+            logger.info("No ROM file specified, loading empty R/W memory image.");
+            this.rom = Memory.makeRAM(ROM_BASE, ROM_BASE + ROM_SIZE - 1);
+        }
+
+        bus.addDevice(rom);
+    }
+
+    @Override
+    public Bus getBus() {
+        return bus;
+    }
+
+    @Override
+    public Cpu getCpu() {
+        return cpu;
+    }
+
+    @Override
+    public Memory getRam() {
+        return ram;
+    }
+
+    @Override
+    public Acia getAcia() {
+        return acia;
+    }
+
+    @Override
+    public Pia getPia() {
+        return null;
+    }
+
+    @Override
+    public Crtc getCrtc() {
+        return null;
+    }
+
+    @Override
+    public Memory getRom() {
+        return rom;
+    }
+    
+    public void setRom(Memory rom) throws MemoryRangeException {
+        if(this.rom != null) {
+            bus.removeDevice(this.rom);
+        }
+        this.rom = rom;
+        bus.addDevice(this.rom);
+    }
+
+    @Override
+    public int getRomBase() {
+        return ROM_BASE;
+    }
+
+    @Override
+    public int getRomSize() {
+        return ROM_SIZE;
+    }
+
+    @Override
+    public int getMemorySize() {
+        return MEMORY_SIZE;
+    }
+
+    @Override
+    public String getName() {
+        return "Multicomp";
+    }
+
+}

src/main/java/com/loomcom/symon/machines/SimpleMachine.java

@@ -0,0 +1,117 @@
+/*
+ * Copyright (c) 2008-2025 Seth J. Morabito <web@loomcom.com>
+ *                         Maik Merten <maikmerten@googlemail.com>
+ *
+ * Permission is hereby granted, free of charge, to any person obtaining
+ * a copy of this software and associated documentation files (the
+ * "Software"), to deal in the Software without restriction, including
+ * without limitation the rights to use, copy, modify, merge, publish,
+ * distribute, sublicense, and/or sell copies of the Software, and to
+ * permit persons to whom the Software is furnished to do so, subject to
+ * the following conditions:
+ *
+ * The above copyright notice and this permission notice shall be
+ * included in all copies or substantial portions of the Software.
+ *
+ * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND,
+ * EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF
+ * MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND
+ * NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS BE
+ * LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION
+ * OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION
+ * WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.
+ */
+
+package com.loomcom.symon.machines;
+
+import com.loomcom.symon.Bus;
+import com.loomcom.symon.Cpu;
+import com.loomcom.symon.devices.Acia;
+import com.loomcom.symon.devices.Crtc;
+import com.loomcom.symon.devices.Memory;
+import com.loomcom.symon.devices.Pia;
+import com.loomcom.symon.exceptions.MemoryRangeException;
+
+/**
+ * A SimpleMachine is the simplest 6502 implementation possible - it
+ * consists solely of RAM and a CPU. This machine is primarily useful
+ * for running 6502 functional tests or debugging by hand.
+ */
+public class SimpleMachine implements Machine {
+
+    private static final int BUS_BOTTOM = 0x0000;
+    private static final int BUS_TOP    = 0xffff;
+
+    private final Bus bus;
+    private final Memory ram;
+    private final Cpu cpu;
+
+    public SimpleMachine(String romFile) throws MemoryRangeException {
+        this.bus = new Bus(BUS_BOTTOM, BUS_TOP);
+        this.ram = new Memory(BUS_BOTTOM, BUS_TOP, false);
+        this.cpu = new Cpu();
+
+        bus.addCpu(cpu);
+        bus.addDevice(ram);
+    }
+
+    @Override
+    public Bus getBus() {
+        return bus;
+    }
+
+    @Override
+    public Cpu getCpu() {
+        return cpu;
+    }
+
+    @Override
+    public Memory getRam() {
+        return ram;
+    }
+
+    @Override
+    public Acia getAcia() {
+        return null;
+    }
+
+    @Override
+    public Pia getPia() {
+        return null;
+    }
+
+    @Override
+    public Crtc getCrtc() {
+        return null;
+    }
+
+    @Override
+    public Memory getRom() {
+        return null;
+    }
+
+    @Override
+    public void setRom(Memory rom) {
+        // No-op
+    }
+
+    @Override
+    public int getRomBase() {
+        return 0;
+    }
+
+    @Override
+    public int getRomSize() {
+        return 0;
+    }
+
+    @Override
+    public int getMemorySize() {
+        return BUS_TOP + 1;
+    }
+
+    @Override
+    public String getName() {
+        return "Simple";
+    }
+}

src/main/java/com/loomcom/symon/machines/SymonMachine.java

@@ -0,0 +1,169 @@
+/*
+ * Copyright (c) 2008-2025 Seth J. Morabito <web@loomcom.com>
+ *                         Maik Merten <maikmerten@googlemail.com>
+ *
+ * Permission is hereby granted, free of charge, to any person obtaining
+ * a copy of this software and associated documentation files (the
+ * "Software"), to deal in the Software without restriction, including
+ * without limitation the rights to use, copy, modify, merge, publish,
+ * distribute, sublicense, and/or sell copies of the Software, and to
+ * permit persons to whom the Software is furnished to do so, subject to
+ * the following conditions:
+ *
+ * The above copyright notice and this permission notice shall be
+ * included in all copies or substantial portions of the Software.
+ *
+ * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND,
+ * EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF
+ * MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND
+ * NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS BE
+ * LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION
+ * OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION
+ * WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.
+ */
+
+package com.loomcom.symon.machines;
+
+import com.loomcom.symon.Bus;
+import com.loomcom.symon.Cpu;
+import com.loomcom.symon.devices.*;
+import com.loomcom.symon.exceptions.MemoryRangeException;
+import org.slf4j.Logger;
+import org.slf4j.LoggerFactory;
+
+import java.io.File;
+
+public class SymonMachine implements Machine {
+    
+    private final static Logger logger = LoggerFactory.getLogger(SymonMachine.class.getName());
+    
+    // Constants used by the simulated system. These define the memory map.
+    private static final int BUS_BOTTOM = 0x0000;
+    private static final int BUS_TOP    = 0xffff;
+
+    // 32K of RAM from $0000 - $7FFF
+    private static final int MEMORY_BASE = 0x0000;
+    private static final int MEMORY_SIZE = 0x8000;
+
+    // PIA at $8000-$800F
+
+    private static final int PIA_BASE = 0x8000;
+
+    // ACIA at $8800-$8803
+    private static final int ACIA_BASE = 0x8800;
+
+    // CRTC at $9000-$9001
+    private static final int CRTC_BASE = 0x9000;
+
+    // 16KB ROM at $C000-$FFFF
+    private static final int ROM_BASE = 0xC000;
+    private static final int ROM_SIZE = 0x4000;
+
+
+        // The simulated peripherals
+    private final Bus    bus;
+    private final Cpu    cpu;
+    private final Acia   acia;
+    private final Pia    pia;
+    private final Crtc   crtc;
+    private final Memory ram;
+    private       Memory rom;
+
+
+    public SymonMachine(String romFile) throws Exception {
+        this.bus = new Bus(BUS_BOTTOM, BUS_TOP);
+        this.cpu = new Cpu();
+        this.ram = new Memory(MEMORY_BASE, MEMORY_BASE + MEMORY_SIZE - 1, false);
+        this.pia = new Via6522(PIA_BASE);
+        this.acia = new Acia6551(ACIA_BASE);
+        this.crtc = new Crtc(CRTC_BASE, ram);
+
+        bus.addCpu(cpu);
+        bus.addDevice(ram);
+        bus.addDevice(pia);
+        bus.addDevice(acia);
+        bus.addDevice(crtc);
+
+        if (romFile != null) {
+            File romImage = new File(romFile);
+            if (romImage.canRead()) {
+                logger.info("Loading ROM image from file {}", romImage);
+                this.rom = Memory.makeROM(ROM_BASE, ROM_BASE + ROM_SIZE - 1, romImage);
+            } else {
+                logger.info("Default ROM file {} not found, loading empty R/W memory image.", romImage);
+                this.rom = Memory.makeRAM(ROM_BASE, ROM_BASE + ROM_SIZE - 1);
+            }
+        } else {
+            logger.info("No ROM file specified, loading empty R/W memory image.");
+            this.rom = Memory.makeRAM(ROM_BASE, ROM_BASE + ROM_SIZE - 1);
+        }
+
+        bus.addDevice(rom);
+        
+    }
+
+    @Override
+    public Bus getBus() {
+        return bus;
+    }
+
+    @Override
+    public Cpu getCpu() {
+        return cpu;
+    }
+
+    @Override
+    public Memory getRam() {
+        return ram;
+    }
+
+    @Override
+    public Acia getAcia() {
+        return acia;
+    }
+
+    @Override
+    public Pia getPia() {
+        return pia;
+    }
+
+    @Override
+    public Crtc getCrtc() {
+        return crtc;
+    }
+
+    @Override
+    public Memory getRom() {
+        return rom;
+    }
+    
+    public void setRom(Memory rom) throws MemoryRangeException {
+        if(this.rom != null) {
+            bus.removeDevice(this.rom);
+        }
+        this.rom = rom;
+        bus.addDevice(this.rom);
+    }
+
+    @Override
+    public int getRomBase() {
+        return ROM_BASE;
+    }
+
+    @Override
+    public int getRomSize() {
+        return ROM_SIZE;
+    }
+
+    @Override
+    public int getMemorySize() {
+        return MEMORY_SIZE;
+    }
+
+    @Override
+    public String getName() {
+        return "Symon";
+    }
+
+
+}

src/main/java/com/loomcom/symon/ui/BreakpointsWindow.java

@@ -0,0 +1,127 @@
+/*
+ * Copyright (c) 2008-2025 Seth J. Morabito <web@loomcom.com>
+ *
+ * Permission is hereby granted, free of charge, to any person obtaining
+ * a copy of this software and associated documentation files (the
+ * "Software"), to deal in the Software without restriction, including
+ * without limitation the rights to use, copy, modify, merge, publish,
+ * distribute, sublicense, and/or sell copies of the Software, and to
+ * permit persons to whom the Software is furnished to do so, subject to
+ * the following conditions:
+ *
+ * The above copyright notice and this permission notice shall be
+ * included in all copies or substantial portions of the Software.
+ *
+ * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND,
+ * EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF
+ * MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND
+ * NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS BE
+ * LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION
+ * OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION
+ * WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.
+ */
+
+package com.loomcom.symon.ui;
+
+import com.loomcom.symon.Breakpoints;
+import com.loomcom.symon.util.Utils;
+import org.slf4j.Logger;
+import org.slf4j.LoggerFactory;
+
+import javax.swing.*;
+import javax.swing.border.EmptyBorder;
+import java.awt.*;
+import java.awt.event.ActionListener;
+
+/**
+ * Simple window to enter breakpoints.
+ */
+public class BreakpointsWindow extends JFrame {
+
+    private static final Logger logger = LoggerFactory.getLogger(BreakpointsWindow.class);
+
+    private static final Dimension FRAME_SIZE = new Dimension(240, 280);
+    private static final String EMPTY_STRING = "";
+
+    private final JFrame mainWindow;
+    private final Breakpoints breakpoints;
+
+    public BreakpointsWindow(Breakpoints breakpoints,
+                             JFrame mainWindow) {
+        this.breakpoints = breakpoints;
+        this.mainWindow = mainWindow;
+        createUi();
+    }
+
+    private void createUi() {
+        setTitle("Breakpoints");
+
+        JPanel breakpointsPanel = new JPanel();
+        JPanel controlPanel = new JPanel();
+
+        breakpointsPanel.setLayout(new BorderLayout());
+        breakpointsPanel.setBorder(new EmptyBorder(10, 10, 10, 10));
+
+        final JButton addButton = new JButton("Add");
+        final JButton removeButton = new JButton("Del");
+        removeButton.setEnabled(false);
+
+        final JTextField addTextField = new JTextField(4);
+
+        final JTable breakpointsTable = new JTable(breakpoints);
+        breakpointsTable.setShowGrid(true);
+        breakpointsTable.setSelectionMode(ListSelectionModel.SINGLE_SELECTION);
+        breakpointsTable.getSelectionModel().addListSelectionListener(e -> removeButton.setEnabled(e.getFirstIndex() > -1));
+
+        JScrollPane scrollPane = new JScrollPane(breakpointsTable);
+        scrollPane.setHorizontalScrollBarPolicy(ScrollPaneConstants.HORIZONTAL_SCROLLBAR_NEVER);
+        scrollPane.setVerticalScrollBarPolicy(ScrollPaneConstants.VERTICAL_SCROLLBAR_ALWAYS);
+
+        breakpointsPanel.add(scrollPane, BorderLayout.CENTER);
+
+        ActionListener addBreakpointListener = e -> {
+            int value;
+
+            String newBreakpoint = addTextField.getText();
+
+            if (newBreakpoint == null || newBreakpoint.isEmpty()) {
+                return;
+            }
+
+            try {
+                value = (Integer.parseInt(addTextField.getText(), 16) & 0xffff);
+            } catch (NumberFormatException ex) {
+                logger.warn("Can't parse page number {}", newBreakpoint);
+                return;
+            }
+
+            breakpoints.addBreakpoint(value);
+
+            logger.debug("Added breakpoint ${}", Utils.wordToHex(value));
+
+            addTextField.setText(EMPTY_STRING);
+        };
+
+        addButton.addActionListener(addBreakpointListener);
+        addTextField.addActionListener(addBreakpointListener);
+
+        removeButton.addActionListener(e -> breakpoints.removeBreakpointAtIndex(breakpointsTable.getSelectedRow()));
+
+        controlPanel.add(addTextField);
+        controlPanel.add(addButton);
+        controlPanel.add(removeButton);
+
+        setLayout(new BorderLayout());
+        getContentPane().add(breakpointsPanel, BorderLayout.CENTER);
+        getContentPane().add(controlPanel, BorderLayout.SOUTH);
+
+        setMinimumSize(FRAME_SIZE);
+        setMaximumSize(FRAME_SIZE);
+        setPreferredSize(FRAME_SIZE);
+
+        setLocationRelativeTo(mainWindow);
+        setResizable(false);
+
+        pack();
+    }
+}

src/main/java/com/loomcom/symon/ui/Console.java

@@ -1,5 +1,5 @@
 /*
- * Copyright (c) 2013 Seth J. Morabito <web@loomcom.com>
+ * Copyright (c) 2008-2025 Seth J. Morabito <web@loomcom.com>
  *
  * Permission is hereby granted, free of charge, to any person obtaining
  * a copy of this software and associated documentation files (the
@@ -23,8 +23,8 @@
 
 package com.loomcom.symon.ui;
 
-import com.grahamedgecombe.jterminal.JTerminal;
-import com.grahamedgecombe.jterminal.vt100.Vt100TerminalModel;
+import com.loomcom.symon.jterminal.JTerminal;
+import com.loomcom.symon.jterminal.vt100.Vt100TerminalModel;
 import com.loomcom.symon.exceptions.FifoUnderrunException;
 import com.loomcom.symon.util.FifoRingBuffer;
 
@@ -44,21 +44,23 @@ import java.awt.event.MouseListener;
 
 public class Console extends JTerminal implements KeyListener, MouseListener {
 
-    private static final int     DEFAULT_COLUMNS      = 80;
-    private static final int     DEFAULT_ROWS         = 24;
-    private static final int     DEFAULT_BORDER_WIDTH = 10;
+	private static final long serialVersionUID = 6633818486963338126L;
+	
+	private static final int     DEFAULT_BORDER_WIDTH = 10;
     // If true, swap CR and LF characters.
     private static final boolean SWAP_CR_AND_LF       = true;
+
     // If true, send CRLF (0x0d 0x0a) whenever CR is typed
-    private static final boolean SEND_CR_LF_FOR_CR    = false;
+    private final boolean sendCrForLf;
+    private final FifoRingBuffer<Character> typeAheadBuffer;
 
-    private FifoRingBuffer<Character> typeAheadBuffer;
-
-    public Console(int columns, int rows, Font font) {
+    public Console(int columns, int rows, Font font, boolean sendCrForLf) {
         super(new Vt100TerminalModel(columns, rows), font);
+    		//super(new Vt100TerminalModel(columns, rows));
         // A small type-ahead buffer, as might be found in any real
         // VT100-style serial terminal.
-        this.typeAheadBuffer = new FifoRingBuffer<Character>(128);
+        this.typeAheadBuffer = new FifoRingBuffer<>(128);
+        this.sendCrForLf = sendCrForLf;
         setBorderWidth(DEFAULT_BORDER_WIDTH);
         addKeyListener(this);
         addMouseListener(this);
@@ -83,7 +85,7 @@ public class Console extends JTerminal implements KeyListener, MouseListener {
     /**
      * Returns true if a key has been pressed since the last time input was read.
      *
-     * @return
+     * @return true if the type-ahead buffer has data
      */
     public boolean hasInput() {
         return !typeAheadBuffer.isEmpty();
@@ -105,7 +107,7 @@ public class Console extends JTerminal implements KeyListener, MouseListener {
             }
         }
 
-        if (SEND_CR_LF_FOR_CR && keyTyped == 0x0d) {
+        if (sendCrForLf && (keyTyped == 0x0d)) {
             typeAheadBuffer.push((char) 0x0d);
             typeAheadBuffer.push((char) 0x0a);
         } else {

src/main/java/com/loomcom/symon/ui/MemoryWindow.java

@@ -1,5 +1,5 @@
 /*
- * Copyright (c) 2013 Seth J. Morabito <web@loomcom.com>
+ * Copyright (c) 2008-2025 Seth J. Morabito <web@loomcom.com>
  *
  * Permission is hereby granted, free of charge, to any person obtaining
  * a copy of this software and associated documentation files (the
@@ -25,7 +25,9 @@ package com.loomcom.symon.ui;
 
 import com.loomcom.symon.Bus;
 import com.loomcom.symon.exceptions.MemoryAccessException;
-import com.loomcom.symon.util.HexUtil;
+import com.loomcom.symon.util.Utils;
+import org.slf4j.Logger;
+import org.slf4j.LoggerFactory;
 
 import javax.swing.*;
 import javax.swing.border.EmptyBorder;
@@ -37,8 +39,7 @@ import java.awt.*;
 import java.awt.event.ActionEvent;
 import java.awt.event.ActionListener;
 import java.util.EventObject;
-import java.util.logging.Level;
-import java.util.logging.Logger;
+
 
 /**
  * This Frame displays the contents of a page of memory. The page number to be displayed
@@ -46,7 +47,9 @@ import java.util.logging.Logger;
  */
 public class MemoryWindow extends JFrame implements ActionListener {
 
-    private MemoryTableModel memoryTableModel;
+    private static final Logger logger = LoggerFactory.getLogger(MemoryWindow.class);
+
+    private final MemoryTableModel memoryTableModel;
     private JTable memoryTable;
     private JTextField pageNumberTextField;
     private JButton previousPageButton;
@@ -104,11 +107,11 @@ public class MemoryWindow extends JFrame implements ActionListener {
 
         previousPageButton.setEnabled(pageNumber > 0x00);
         nextPageButton.setEnabled(pageNumber < 0xff);
-        pageNumberTextField.setText(HexUtil.byteToHex(pageNumber));
+        pageNumberTextField.setText(Utils.byteToHex(pageNumber));
     }
 
     /**
-     * Set-up the UI.
+     * Set up the UI.
      */
     private void createUi() {
         setTitle("Memory Contents");
@@ -190,14 +193,14 @@ public class MemoryWindow extends JFrame implements ActionListener {
             if (currentPage > 0x00) {
                 setPageNumber(currentPage - 1);
                 updateControls();
-                memoryTable.updateUI();
+                updateState();
             }
         } else if (e.getSource() == nextPageButton) {
             int currentPage = getPageNumber();
             if (currentPage < 0xff) {
                 setPageNumber(currentPage + 1);
                 updateControls();
-                memoryTable.updateUI();
+                updateState();
             }
         } else if (e.getSource() == pageNumberTextField) {
             String pageNumberInput = pageNumberTextField.getText();
@@ -205,22 +208,29 @@ public class MemoryWindow extends JFrame implements ActionListener {
                 // Try to parse a hex value out of the pageNumber.
                 int newPageNumber = Integer.parseInt(pageNumberInput, 16);
                 setPageNumber(newPageNumber & 0xff);
-                memoryTable.updateUI();
+                updateState();
             } catch (NumberFormatException ex) {
                 // An invalid number was entered. Log the error, but otherwise
                 // take no action.
-                Logger.getLogger(this.getClass().getName()).log(Level.WARNING, "Can't parse page number " +
-                        pageNumberInput);
+                logger.warn("Can't parse page number {}", pageNumberInput);
             }
+
             updateControls();
         }
     }
 
+    /**
+     * Refresh the view of memory
+     */
+    public void updateState() {
+        memoryTable.updateUI();
+    }
+
     /**
      * A JTable that will automatically select all text in a cell
      * being edited.
      */
-    private class MemoryTable extends JTable {
+    private static class MemoryTable extends JTable {
 
         public MemoryTable(TableModel tableModel) {
             super(tableModel);
@@ -232,7 +242,7 @@ public class MemoryWindow extends JFrame implements ActionListener {
 
             final Component editor = getEditorComponent();
 
-            if (editor != null && editor instanceof JTextComponent) {
+            if (editor instanceof JTextComponent) {
                 ((JTextComponent) editor).selectAll();
             }
 
@@ -240,7 +250,7 @@ public class MemoryWindow extends JFrame implements ActionListener {
         }
     }
 
-    private class MemoryTableCellRenderer extends DefaultTableCellRenderer {
+    private static class MemoryTableCellRenderer extends DefaultTableCellRenderer {
 
         @Override
         public Component getTableCellRendererComponent(JTable table, Object value,
@@ -262,9 +272,9 @@ public class MemoryWindow extends JFrame implements ActionListener {
     /**
      * The model that backs the Memory Table.
      */
-    private class MemoryTableModel extends AbstractTableModel {
+    private static class MemoryTableModel extends AbstractTableModel {
 
-        private Bus bus;
+        private final Bus bus;
         private int pageNumber;
 
         private static final int COLUMN_COUNT = 17;
@@ -318,13 +328,13 @@ public class MemoryWindow extends JFrame implements ActionListener {
         public Object getValueAt(int row, int column) {
             try {
                 if (column == 0) {
-                    return HexUtil.wordToHex(fullAddress(row, 1));
+                    return Utils.wordToHex(fullAddress(row, 1));
                 } else if (column < 9) {
                     // Display hex value of the data
-                    return HexUtil.byteToHex(bus.read(fullAddress(row, column)));
+                    return Utils.byteToHex(bus.read(fullAddress(row, column), false));
                 } else {
                     // Display the ASCII equivalent (if printable)
-                    return HexUtil.byteToAscii(bus.read(fullAddress(row, column - 8)));
+                    return Utils.byteToAscii(bus.read(fullAddress(row, column - 8), false));
                 }
             } catch (MemoryAccessException ex) {
                 return "??";
@@ -339,12 +349,8 @@ public class MemoryWindow extends JFrame implements ActionListener {
                     int fullAddress = fullAddress(row, column);
                     int newValue = Integer.parseInt(hexValue, 16) & 0xff;
                     bus.write(fullAddress, newValue);
-                } catch (MemoryAccessException ex) {
-                    ;
-                } catch (NumberFormatException ex) {
-                    ;
-                } catch (ClassCastException ex) {
-                    ;
+                } catch (MemoryAccessException | NumberFormatException | ClassCastException ex) {
+                    // Intentionally swallow exception
                 }
                 fireTableCellUpdated(row, column);
             }

src/main/java/com/loomcom/symon/ui/PreferencesDialog.java

@@ -1,5 +1,5 @@
 /*
- * Copyright (c) 2013 Seth J. Morabito <web@loomcom.com>
+ * Copyright (c) 2008-2025 Seth J. Morabito <web@loomcom.com>
  *
  * Permission is hereby granted, free of charge, to any person obtaining
  * a copy of this software and associated documentation files (the
@@ -42,11 +42,11 @@ public class PreferencesDialog extends Observable implements Preferences {
     private JTextField programLoadAddressField;
 
     private int programLoadAddress = DEFAULT_PROGRAM_LOAD_ADDRESS;
-    private boolean haltOnBreak = DEFAULT_HALT_ON_BREAK;
+    private boolean haltOnBreak;
 
-    public PreferencesDialog(Frame parent, boolean modal) {
+    public PreferencesDialog(Frame parent, boolean modal, boolean haltOnBreak) {
         this.dialog = new JDialog(parent, modal);
-
+        this.haltOnBreak = haltOnBreak;
         createUi();
         updateUi();
     }
@@ -98,19 +98,21 @@ public class PreferencesDialog extends Observable implements Preferences {
         JButton cancelButton = new JButton("Cancel");
 
         cancelButton.addActionListener(new ActionListener() {
+            @Override
             public void actionPerformed(ActionEvent actionEvent) {
-                updateUi();
+                PreferencesDialog.this.updateUi();
                 dialog.setVisible(false);
             }
         });
 
         applyButton.addActionListener(new ActionListener() {
+            @Override
             public void actionPerformed(ActionEvent actionEvent) {
                 haltOnBreak = haltOnBreakCheckBox.isSelected();
-                programLoadAddress = hexToInt(programLoadAddressField.getText());
-                updateUi();
+                programLoadAddress = PreferencesDialog.this.hexToInt(programLoadAddressField.getText());
+                PreferencesDialog.this.updateUi();
                 // TODO: Actually check to see if values have changed, don't assume.
-                setChanged();
+                PreferencesDialog.this.setChanged();
                 PreferencesDialog.this.notifyObservers();
                 dialog.setVisible(false);
             }

src/main/java/com/loomcom/symon/ui/StatusPanel.java

@@ -1,5 +1,5 @@
 /*
- * Copyright (c) 2013 Seth J. Morabito <web@loomcom.com>
+ * Copyright (c) 2008-2025 Seth J. Morabito <web@loomcom.com>
  *
  * Permission is hereby granted, free of charge, to any person obtaining
  * a copy of this software and associated documentation files (the
@@ -23,12 +23,20 @@
 
 package com.loomcom.symon.ui;
 
+import com.formdev.flatlaf.util.UIScale;
 import com.loomcom.symon.Cpu;
+import com.loomcom.symon.CpuState;
+import com.loomcom.symon.devices.Pia;
+import com.loomcom.symon.devices.Via6522;
+import com.loomcom.symon.machines.Machine;
 
 import javax.swing.*;
 import javax.swing.border.Border;
 import javax.swing.border.EtchedBorder;
 import java.awt.*;
+import java.awt.event.ActionEvent;
+import java.awt.event.ActionListener;
+import java.util.Objects;
 
 /**
  * UI component that displays the current state of the simulated CPU.
@@ -50,7 +58,6 @@ public class StatusPanel extends JPanel {
     private ImageIcon negativeOn;
     private ImageIcon negativeOff;
 
-    private JLabel statusFlagsLabel;
     private JLabel carryFlagLabel;
     private JLabel zeroFlagLabel;
     private JLabel irqDisableFlagLabel;
@@ -65,28 +72,26 @@ public class StatusPanel extends JPanel {
     private JTextField aField;
     private JTextField xField;
     private JTextField yField;
+    private JTextField piaBField;
+    private JTextField piaAField;
 
-    private JLabel opcodeLabel;
-    private JLabel pcLabel;
-    private JLabel spLabel;
-    private JLabel aLabel;
-    private JLabel xLabel;
-    private JLabel yLabel;
+    private final Machine machine;
 
     private static final int EMPTY_BORDER = 10;
     private static final Border LABEL_BORDER = BorderFactory.createEmptyBorder(0, 5, 0, 0);
-    private static final Font LABEL_FONT = new Font(Font.SANS_SERIF, Font.BOLD, 12);
+    private static final Font LABEL_FONT = new Font(Font.SANS_SERIF, Font.BOLD, UIScale.scale(12));
     private static final Dimension LARGE_TEXT_FIELD_SIZE = new Dimension(134, 22);
     private static final Dimension SMALL_TEXT_FIELD_SIZE = new Dimension(65, 22);
 
-    public StatusPanel() {
+    public StatusPanel(Machine machine) {
         super();
+        this.machine = machine;
         createUi();
     }
 
     private void createUi() {
         Border emptyBorder = BorderFactory.createEmptyBorder(EMPTY_BORDER, EMPTY_BORDER,
-                                                             EMPTY_BORDER, EMPTY_BORDER);
+                EMPTY_BORDER, EMPTY_BORDER);
         Border etchedBorder = BorderFactory.createEtchedBorder(EtchedBorder.LOWERED);
 
         setBorder(BorderFactory.createCompoundBorder(emptyBorder, etchedBorder));
@@ -99,20 +104,20 @@ public class StatusPanel extends JPanel {
         JPanel statusFlagsPanel = new JPanel();
         statusFlagsPanel.setAlignmentX(LEFT_ALIGNMENT);
 
-        carryOn = new ImageIcon(this.getClass().getResource("images/C_on.png"));
-        carryOff = new ImageIcon(this.getClass().getResource("images/C_off.png"));
-        zeroOn = new ImageIcon(this.getClass().getResource("images/Z_on.png"));
-        zeroOff = new ImageIcon(this.getClass().getResource("images/Z_off.png"));
-        irqOn = new ImageIcon(this.getClass().getResource("images/I_on.png"));
-        irqOff = new ImageIcon(this.getClass().getResource("images/I_off.png"));
-        decimalOn = new ImageIcon(this.getClass().getResource("images/D_on.png"));
-        decimalOff = new ImageIcon(this.getClass().getResource("images/D_off.png"));
-        breakOn = new ImageIcon(this.getClass().getResource("images/B_on.png"));
-        breakOff = new ImageIcon(this.getClass().getResource("images/B_off.png"));
-        overflowOn = new ImageIcon(this.getClass().getResource("images/O_on.png"));
-        overflowOff = new ImageIcon(this.getClass().getResource("images/O_off.png"));
-        negativeOn = new ImageIcon(this.getClass().getResource("images/N_on.png"));
-        negativeOff = new ImageIcon(this.getClass().getResource("images/N_off.png"));
+        carryOn = loadScaledIcon("/C_on.png");
+        carryOff = loadScaledIcon("/C_off.png");
+        zeroOn = loadScaledIcon("/Z_on.png");
+        zeroOff = loadScaledIcon("/Z_off.png");
+        irqOn = loadScaledIcon("/I_on.png");
+        irqOff = loadScaledIcon("/I_off.png");
+        decimalOn = loadScaledIcon("/D_on.png");
+        decimalOff = loadScaledIcon("/D_off.png");
+        breakOn = loadScaledIcon("/B_on.png");
+        breakOff = loadScaledIcon("/B_off.png");
+        overflowOn = loadScaledIcon("/O_on.png");
+        overflowOff = loadScaledIcon("/O_off.png");
+        negativeOn = loadScaledIcon("/N_on.png");
+        negativeOff = loadScaledIcon("/N_off.png");
 
         // Initialize all to off
         carryFlagLabel = new JLabel(carryOff, JLabel.CENTER);
@@ -125,16 +130,15 @@ public class StatusPanel extends JPanel {
 
         // Add tool-tip text
         carryFlagLabel.setToolTipText("Carry: The last operation caused an overflow " +
-                                      "from bit 7 of the result or an underflow from bit 0");
+                "from bit 7 of the result or an underflow from bit 0");
         zeroFlagLabel.setToolTipText("Zero: The result of the last operation was 0");
         irqDisableFlagLabel.setToolTipText("Interrupt Disable: Processor will not respond to IRQ");
         decimalModeFlagLabel.setToolTipText("Decimal Mode");
         breakFlagLabel.setToolTipText("Break: BRK instruction occurred");
         overflowFlagLabel.setToolTipText("Overflow: The result of the last operation was " +
-                                         "an invalid 2's complement result");
+                "an invalid 2's complement result");
         negativeFlagLabel.setToolTipText("Negative: The result of the last operation set bit 7");
 
-
         statusFlagsPanel.add(negativeFlagLabel);
         statusFlagsPanel.add(overflowFlagLabel);
         statusFlagsPanel.add(breakFlagLabel);
@@ -144,25 +148,103 @@ public class StatusPanel extends JPanel {
         statusFlagsPanel.add(carryFlagLabel);
 
         // Create and add register and address labels
-        statusFlagsLabel = makeLabel("Flags");
-        opcodeLabel = makeLabel("IR");
-        pcLabel = makeLabel("PC");
-        spLabel = makeLabel("SP");
-        aLabel = makeLabel("A");
-        xLabel = makeLabel("X");
-        yLabel = makeLabel("Y");
+        JLabel statusFlagsLabel = makeLabel("Flags");
+        JLabel opcodeLabel = makeLabel("Next IR");
+        JLabel pcLabel = makeLabel("PC");
+        JLabel spLabel = makeLabel("SP");
+        JLabel aLabel = makeLabel("A");
+        JLabel xLabel = makeLabel("X");
+        JLabel yLabel = makeLabel("Y");
+
+        // PIA/VIA labels
+        JLabel piaBLabel = makeLabel("PB");
+        JLabel piaALabel = makeLabel("PA");
 
         statusFlagsLabel.setToolTipText("6502 Processor Status Flags");
         opcodeLabel.setToolTipText("Instruction Register");
         pcLabel.setToolTipText("Program Counter");
         spLabel.setToolTipText("Stack Pointer");
 
-        opcodeField = makeTextField(LARGE_TEXT_FIELD_SIZE);
-        pcField = makeTextField(LARGE_TEXT_FIELD_SIZE);
-        spField = makeTextField(SMALL_TEXT_FIELD_SIZE);
-        aField = makeTextField(SMALL_TEXT_FIELD_SIZE);
-        xField = makeTextField(SMALL_TEXT_FIELD_SIZE);
-        yField = makeTextField(SMALL_TEXT_FIELD_SIZE);
+        opcodeField = makeTextField(LARGE_TEXT_FIELD_SIZE, false);
+        pcField = makeTextField(LARGE_TEXT_FIELD_SIZE, true);
+        spField = makeTextField(SMALL_TEXT_FIELD_SIZE, true);
+        aField = makeTextField(SMALL_TEXT_FIELD_SIZE, true);
+        xField = makeTextField(SMALL_TEXT_FIELD_SIZE, true);
+        yField = makeTextField(SMALL_TEXT_FIELD_SIZE, true);
+
+        piaBField = makeTextField(LARGE_TEXT_FIELD_SIZE, false);
+        piaAField = makeTextField(LARGE_TEXT_FIELD_SIZE, false);
+
+        // Make fields editable
+        pcField.addActionListener(new ActionListener() {
+            @Override
+            public void actionPerformed(ActionEvent e) {
+                try {
+                    int newVal = StatusPanel.this.getHexVal(pcField) & 0xffff;
+                    machine.getCpu().setProgramCounter(newVal);
+                } catch (Exception ex) {
+                    // Swallow exception
+                }
+
+                StatusPanel.this.updateState();
+            }
+        });
+
+        spField.addActionListener(new ActionListener() {
+            @Override
+            public void actionPerformed(ActionEvent e) {
+                try {
+                    int newVal = StatusPanel.this.getHexVal(spField) & 0xff;
+                    machine.getCpu().setStackPointer(newVal);
+                } catch (Exception ex) {
+                    // Swallow exception
+                }
+
+                StatusPanel.this.updateState();
+            }
+        });
+
+        aField.addActionListener(new ActionListener() {
+            @Override
+            public void actionPerformed(ActionEvent e) {
+                try {
+                    int newVal = StatusPanel.this.getHexVal(aField) & 0xff;
+                    machine.getCpu().setAccumulator(newVal);
+                } catch (Exception ex) {
+                    // Swallow exception
+                }
+
+                StatusPanel.this.updateState();
+            }
+        });
+
+        xField.addActionListener(new ActionListener() {
+            @Override
+            public void actionPerformed(ActionEvent e) {
+                try {
+                    int newVal = StatusPanel.this.getHexVal(xField) & 0xff;
+                    machine.getCpu().setXRegister(newVal);
+                } catch (Exception ex) {
+                    // Swallow exception
+                }
+
+                StatusPanel.this.updateState();
+            }
+        });
+
+        yField.addActionListener(new ActionListener() {
+            @Override
+            public void actionPerformed(ActionEvent e) {
+                try {
+                    int newVal = StatusPanel.this.getHexVal(yField) & 0xff;
+                    machine.getCpu().setYRegister(newVal);
+                } catch (Exception ex) {
+                    // Swallow exception
+                }
+
+                StatusPanel.this.updateState();
+            }
+        });
 
         constraints.anchor = GridBagConstraints.LINE_START;
         constraints.gridwidth = 2;
@@ -172,7 +254,6 @@ public class StatusPanel extends JPanel {
         constraints.gridy = 1;
         add(statusFlagsPanel, constraints);
 
-
         constraints.insets = new Insets(5, 0, 0, 0);
         constraints.gridy = 2;
         add(opcodeLabel, constraints);
@@ -216,18 +297,38 @@ public class StatusPanel extends JPanel {
         add(xField, constraints);
         constraints.gridx = 1;
         add(yField, constraints);
+
+        constraints.insets = new Insets(5, 0, 0, 0);
+        constraints.gridx = 0;
+        constraints.gridwidth = 2;
+        constraints.gridy = 10;
+        add(piaBLabel, constraints);
+
+        constraints.insets = new Insets(2, 2, 2, 2);
+        constraints.gridy = 11;
+        add(piaBField, constraints);
+
+        constraints.insets = new Insets(5, 0, 0, 0);
+        constraints.gridy = 12;
+        add(piaALabel, constraints);
+
+        constraints.insets = new Insets(2, 2, 2, 2);
+        constraints.gridy = 13;
+        add(piaAField, constraints);
+
     }
 
     /**
      * Update the display based on the current state of the CPU.
-     *
-     * @param cpu The simulated 6502 CPU.
      */
-    public void updateState(Cpu cpu) {
-        Cpu.CpuState cpuState = cpu.getCpuState();
+    public void updateState() {
+        Cpu cpu = machine.getCpu();
+        CpuState cpuState = cpu.getCpuState();
+
+        Pia pia = machine.getPia();
 
         // Update the Processor Status Flag display
-        int status = cpu.getCpuState().getStatusFlag();
+        int status = cpuState.getStatusFlag();
 
         carryFlagLabel.setIcon(iconForFlag(status, 0));
         zeroFlagLabel.setIcon(iconForFlag(status, 1));
@@ -238,13 +339,21 @@ public class StatusPanel extends JPanel {
         negativeFlagLabel.setIcon(iconForFlag(status, 7));
 
         // Update the register and address displays
-        opcodeField.setText(cpu.getCpuState().disassembleOp());
+
+        // We always want to show the NEXT instruction that will be executed
+        opcodeField.setText(cpu.disassembleNextOp());
         pcField.setText(cpu.getProgramCounterStatus());
         spField.setText(cpu.getStackPointerStatus());
         aField.setText(cpu.getAccumulatorStatus());
         xField.setText(cpu.getXRegisterStatus());
         yField.setText(cpu.getYRegisterStatus());
 
+        // Update the Pia Variables
+        if (pia instanceof Via6522) {
+            piaBField.setText(((Via6522) pia).getPBStatus());
+            piaAField.setText(((Via6522) pia).getPAStatus());
+        }
+
         repaint();
     }
 
@@ -313,15 +422,31 @@ public class StatusPanel extends JPanel {
         return label;
     }
 
-    private JTextField makeTextField(Dimension size) {
+    private JTextField makeTextField(Dimension size, boolean editable) {
         JTextField textField = new JTextField("");
         textField.setAlignmentX(LEFT_ALIGNMENT);
-        textField.setEditable(false);
-        textField.setMinimumSize(size);
-        textField.setMaximumSize(size);
-        textField.setPreferredSize(size);
-        textField.setBackground(Color.WHITE);
+        textField.setEditable(editable);
+
+        Dimension scaleSize = UIScale.scale(size);
+        textField.setMinimumSize(scaleSize);
+        textField.setMaximumSize(scaleSize);
+        textField.setPreferredSize(scaleSize);
+
         return textField;
     }
 
+    private int getHexVal(JTextField source) throws NumberFormatException {
+        String val = source.getText().replaceAll("[^0-9a-fA-F]", "");
+        return Integer.parseInt(val, 16);
+    }
+
+    private ImageIcon loadScaledIcon(String resourcePath) {
+        ImageIcon icon = new ImageIcon(Objects.requireNonNull(this.getClass().getResource(resourcePath)));
+
+        int scaledWidth = UIScale.scale(icon.getIconWidth());
+        int scaledHeight = UIScale.scale(icon.getIconHeight());
+
+        Image scaleImage = icon.getImage().getScaledInstance(scaledWidth, scaledHeight, Image.SCALE_SMOOTH);
+        return new ImageIcon(scaleImage);
+    }
 }

src/main/java/com/loomcom/symon/ui/TraceLog.java

@@ -1,5 +1,6 @@
 /*
- * Copyright (c) 2013 Seth J. Morabito <web@loomcom.com>
+ * Copyright (c) 2008-2025 Seth J. Morabito <web@loomcom.com>
+ *                         Maik Merten <maikmerten@googlemail.com>
  *
  * Permission is hereby granted, free of charge, to any person obtaining
  * a copy of this software and associated documentation files (the
@@ -23,7 +24,7 @@
 
 package com.loomcom.symon.ui;
 
-import com.loomcom.symon.Cpu;
+import com.loomcom.symon.CpuState;
 import com.loomcom.symon.util.FifoRingBuffer;
 
 import javax.swing.*;
@@ -35,15 +36,15 @@ import java.awt.*;
  */
 public class TraceLog extends JFrame {
 
-    private FifoRingBuffer<Cpu.CpuState> traceLog;
-    private JTextArea                    traceLogTextArea;
+    private final FifoRingBuffer<CpuState> traceLog;
+    private final JTextArea                    traceLogTextArea;
 
     private static final Dimension MIN_SIZE       = new Dimension(320, 200);
     private static final Dimension PREFERRED_SIZE = new Dimension(640, 480);
     private static final int       MAX_LOG_LENGTH = 50000;
 
     public TraceLog() {
-        traceLog = new FifoRingBuffer<Cpu.CpuState>(MAX_LOG_LENGTH);
+        traceLog = new FifoRingBuffer<>(MAX_LOG_LENGTH);
         setMinimumSize(MIN_SIZE);
         setPreferredSize(PREFERRED_SIZE);
         setResizable(true);
@@ -67,11 +68,15 @@ public class TraceLog extends JFrame {
      * call.
      */
     public void refresh() {
-        synchronized (this) {
-            StringBuilder logString = new StringBuilder();
-            for (Cpu.CpuState state : traceLog) {
+        StringBuilder logString = new StringBuilder();        
+        
+        synchronized(traceLog) {
+            for (CpuState state : traceLog) {
                 logString.append(state.toTraceEvent());
             }
+        }
+
+        synchronized(traceLogTextArea) {
             traceLogTextArea.setText(logString.toString());
         }
     }
@@ -80,8 +85,10 @@ public class TraceLog extends JFrame {
      * Reset the log area.
      */
     public void reset() {
-        synchronized (this) {
+        synchronized(traceLog) {
             traceLog.reset();
+        }
+        synchronized(traceLogTextArea) {
             traceLogTextArea.setText("");
             traceLogTextArea.setEnabled(true);
         }
@@ -92,9 +99,9 @@ public class TraceLog extends JFrame {
      *
      * @param state The CPU State to append.
      */
-    public void append(Cpu.CpuState state) {
-        synchronized(this) {
-            traceLog.push(new Cpu.CpuState(state));
+    public void append(CpuState state) {
+        synchronized(traceLog) {
+            traceLog.push(new CpuState(state));
         }
     }
 
@@ -106,4 +113,8 @@ public class TraceLog extends JFrame {
         traceLogTextArea.setEnabled(true);
     }
 
+    public boolean shouldUpdate() {
+        return isVisible() && traceLogTextArea.isEnabled();
+    }
+
 }

src/main/java/com/loomcom/symon/ui/Ui.java

@@ -0,0 +1,153 @@
+/*
+ * Copyright (c) 2008-2025 Seth J. Morabito <web@loomcom.com>
+ *
+ * Permission is hereby granted, free of charge, to any person obtaining
+ * a copy of this software and associated documentation files (the
+ * "Software"), to deal in the Software without restriction, including
+ * without limitation the rights to use, copy, modify, merge, publish,
+ * distribute, sublicense, and/or sell copies of the Software, and to
+ * permit persons to whom the Software is furnished to do so, subject to
+ * the following conditions:
+ *
+ * The above copyright notice and this permission notice shall be
+ * included in all copies or substantial portions of the Software.
+ *
+ * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND,
+ * EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF
+ * MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND
+ * NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS BE
+ * LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION
+ * OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION
+ * WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.
+ */
+
+package com.loomcom.symon.ui;
+
+import javax.swing.JDialog;
+import javax.swing.JFrame;
+import javax.swing.JOptionPane;
+import javax.swing.LookAndFeel;
+import javax.swing.UIManager;
+import javax.swing.UnsupportedLookAndFeelException;
+
+import com.loomcom.symon.machines.*;
+import org.slf4j.Logger;
+import org.slf4j.LoggerFactory;
+
+import com.formdev.flatlaf.FlatDarkLaf;
+import com.formdev.flatlaf.FlatLaf;
+import com.formdev.flatlaf.FlatLightLaf;
+import com.formdev.flatlaf.util.SystemInfo;
+import com.jthemedetecor.OsThemeDetector;
+
+import java.awt.*;
+import java.beans.PropertyChangeListener;
+import java.lang.reflect.InvocationTargetException;
+import java.util.concurrent.CountDownLatch;
+import java.util.concurrent.TimeUnit;
+import java.util.concurrent.atomic.AtomicReference;
+
+public final class Ui {
+    private final static Logger logger = LoggerFactory.getLogger(Ui.class.getName());
+
+    public static void initUi() throws UnsupportedLookAndFeelException {
+        // Location of properties resources for app-specific UI defaults:
+        FlatLaf.registerCustomDefaultsSource("com.loomcom.symon.themes");
+
+        logger.debug("AWT Toolkit class: {}", Toolkit.getDefaultToolkit().getClass().getName());
+
+        // Enable automatic scaling, based on system DPI settings:
+        //System.setProperty("sun.java2d.uiScale.enabled", "true");
+        //System.setProperty("sun.java2d.uiScale", "1x");
+        //System.setProperty("flatlaf.uiScale", "1x");
+
+        applyDetectedUiScale();
+
+        // OS-specific tweaking:
+
+        if (SystemInfo.isLinux) {
+            logger.debug("Adapting UI for Linux.");
+
+            // Enable custom window decorations:
+            JFrame.setDefaultLookAndFeelDecorated(true);
+            JDialog.setDefaultLookAndFeelDecorated(true);
+        }
+
+        else if (SystemInfo.isMacOS) {
+            logger.debug("Adapting UI for MacOS.");
+
+            // Move menu bar from JFrame window to top of screen:
+            System.setProperty("apple.laf.useScreenMenuBar", "true");
+            // Set name used in screen menu bar (first menu after Apple menu):
+            System.setProperty("apple.awt.application.name", "Symon");
+            // Use current macOS appearance (light/dark) for window title bars:
+            System.setProperty("apple.awt.application.appearance", "system");
+        }
+
+        else if (SystemInfo.isWindows) {
+            logger.debug("Adapting UI for Windows.");
+        }
+
+        UIManager.setLookAndFeel(createLookAndFeel());
+    }
+
+    public static Class<?> showMachineSelectionDialog() {
+        Object[] possibilities = { "Symon", "Multicomp", "Simple", "BenEater", "Mike42" };
+        String s = (String) JOptionPane.showInputDialog(
+                null,
+                "Please choose the machine type to be emulated:",
+                "Machine selection",
+                JOptionPane.PLAIN_MESSAGE,
+                null,
+                possibilities,
+                "Symon");
+
+        if (s != null && s.equals("Multicomp")) {
+            return MulticompMachine.class;
+        } else if (s != null && s.equals("Simple")) {
+            return SimpleMachine.class;
+        } else if (s != null && s.equals("BenEater")) {
+            return BenEaterMachine.class;
+        } else if (s != null && s.equals("Mike42")) {
+            return MichaelBillingtonMachine.class;
+        } else {
+            return SymonMachine.class;
+        }
+    }
+
+    private static LookAndFeel createLookAndFeel() {
+        final OsThemeDetector themeDetector = OsThemeDetector.getDetector();
+        final boolean systemThemeIsDark = themeDetector.isDark();
+
+        // Set light/dark mode depending on what can be detected from the system theme:
+        FlatLaf theme;
+        if (systemThemeIsDark) {
+            logger.debug("Using DARK theme.");
+            theme = new FlatDarkLaf();
+        } else {
+            logger.debug("Using LIGHT theme.");
+            theme = new FlatLightLaf();
+        }
+        return theme;
+    }
+
+    private static void applyDetectedUiScale() {
+        Double rawScale = null;
+
+        if (SystemInfo.isLinux) rawScale = X11ResourceReader.readXftDpiScale(); // ex: 1.5, 2.0, 2.5...
+
+        if (rawScale != null && rawScale > 1.0) {
+            // flatlaf.uiScale aceita frações — mantém a precisão original
+            System.setProperty("flatlaf.uiScale", rawScale + "x");
+
+            // sun.java2d.uiScale só aceita inteiros — arredonda para cima
+            int javaScale = (int) Math.ceil(rawScale);
+            //System.setProperty("sun.java2d.uiScale", String.valueOf(javaScale));
+
+            logger.debug("Detected scale {}x, applying flatlaf.uiScale={}x, sun.java2d.uiScale={}x",
+                    rawScale, rawScale, javaScale);
+        } else {
+            logger.debug("No X11 HiDPI scale detected, using default.");
+        }
+    }
+}

src/main/java/com/loomcom/symon/ui/VideoWindow.java

@@ -1,5 +1,5 @@
 /*
- * Copyright (c) 2013 Seth J. Morabito <web@loomcom.com>
+ * Copyright (c) 2008-2025 Seth J. Morabito <web@loomcom.com>
  *
  * Permission is hereby granted, free of charge, to any person obtaining
  * a copy of this software and associated documentation files (the
@@ -25,6 +25,7 @@ package com.loomcom.symon.ui;
 
 import com.loomcom.symon.devices.Crtc;
 import com.loomcom.symon.devices.DeviceChangeListener;
+import com.loomcom.symon.exceptions.MemoryAccessException;
 
 import javax.swing.*;
 import java.awt.*;
@@ -36,8 +37,11 @@ import java.util.concurrent.Executors;
 import java.util.concurrent.ScheduledExecutorService;
 import java.util.concurrent.ScheduledFuture;
 import java.util.concurrent.TimeUnit;
+import java.util.logging.Level;
 import java.util.logging.Logger;
 
+import static java.lang.System.*;
+
 /**
  * VideoWindow represents a graphics framebuffer backed by a 6545 CRTC.
  * Each time the window's VideoPanel is repainted, the video memory is
@@ -57,15 +61,16 @@ public class VideoWindow extends JFrame implements DeviceChangeListener {
 
     private static final Logger logger = Logger.getLogger(VideoWindow.class.getName());
 
+    private static final long WINDOW_REPAINT_INTERVAL = 66; // 30fps rate
     private static final int CHAR_WIDTH = 8;
     private static final int CHAR_HEIGHT = 8;
+    private static final String ASCII_ROM = "/ascii.rom";
 
     private final int scaleX, scaleY;
     private final boolean shouldScale;
 
     private BufferedImage image;
-    private int[] charRom;
-    private int[] videoRam;
+    private final int[] charRom;
 
     private int horizontalDisplayed;
     private int verticalDisplayed;
@@ -74,9 +79,9 @@ public class VideoWindow extends JFrame implements DeviceChangeListener {
     private boolean hideCursor;
 
     private Dimension dimensions;
-    private Crtc crtc;
+    private final Crtc crtc;
 
-    private ScheduledExecutorService scheduler;
+    private final ScheduledExecutorService scheduler;
     private ScheduledFuture<?> cursorBlinker;
 
     /**
@@ -85,17 +90,21 @@ public class VideoWindow extends JFrame implements DeviceChangeListener {
     private class VideoPanel extends JPanel {
         @Override
         public void paintComponent(Graphics g) {
-            for (int i = 0; i < crtc.getPageSize(); i++) {
-                int address = crtc.getStartAddress() + i;
-                int originX = (i % horizontalDisplayed) * CHAR_WIDTH;
-                int originY = (i / horizontalDisplayed) * scanLinesPerRow;
-                image.getRaster().setPixels(originX, originY, CHAR_WIDTH, scanLinesPerRow, getGlyph(address));
+            try {
+                for (int i = 0; i < crtc.getPageSize(); i++) {
+                    int address = crtc.getStartAddress() + i;
+                    int originX = (i % horizontalDisplayed) * CHAR_WIDTH;
+                    int originY = (i / horizontalDisplayed) * scanLinesPerRow;
+                    image.getRaster().setPixels(originX, originY, CHAR_WIDTH, scanLinesPerRow, getGlyph(address));
+                }
+                Graphics2D g2d = (Graphics2D) g;
+                if (shouldScale) {
+                    g2d.scale(scaleX, scaleY);
+                }
+                g2d.drawImage(image, 0, 0, null);
+            } catch (MemoryAccessException ex) {
+                logger.log(Level.SEVERE, "Memory Access Exception, can't paint video window! " + ex.getMessage());
             }
-            Graphics2D g2d = (Graphics2D)g;
-            if (shouldScale) {
-                g2d.scale(scaleX, scaleY);
-            }
-            g2d.drawImage(image, 0, 0, null);
         }
 
         @Override
@@ -115,12 +124,19 @@ public class VideoWindow extends JFrame implements DeviceChangeListener {
      */
     private class CursorBlinker implements Runnable {
         public void run() {
-            SwingUtilities.invokeLater(new Runnable() {
-                public void run() {
-                    if (cursorBlinkRate > 0) {
-                        hideCursor = !hideCursor;
-                        repaint();
-                    }
+            SwingUtilities.invokeLater(() -> {
+                if (cursorBlinkRate > 0) {
+                    hideCursor = !hideCursor;
+                }
+            });
+        }
+    }
+
+    private class WindowPainter implements Runnable {
+        public void run() {
+            SwingUtilities.invokeLater(() -> {
+                if (VideoWindow.this.isVisible()) {
+                    VideoWindow.this.repaint();
                 }
             });
         }
@@ -131,8 +147,7 @@ public class VideoWindow extends JFrame implements DeviceChangeListener {
 
         this.scheduler = Executors.newSingleThreadScheduledExecutor();
         this.crtc = crtc;
-        this.charRom = loadCharRom("/pet.rom");
-        this.videoRam = crtc.getDmaAccess();
+        this.charRom = loadCharRom();
         this.scaleX = scaleX;
         this.scaleY = scaleY;
         this.shouldScale = (scaleX > 1 || scaleY > 1);
@@ -145,6 +160,11 @@ public class VideoWindow extends JFrame implements DeviceChangeListener {
                                                                TimeUnit.MILLISECONDS);
         }
 
+        scheduler.scheduleAtFixedRate(new WindowPainter(),
+                WINDOW_REPAINT_INTERVAL,
+                WINDOW_REPAINT_INTERVAL,
+                TimeUnit.MILLISECONDS);
+
         // Capture some state from the CRTC that will define the
         // window size. When these values change, the window will
         // need to re-pack and redraw.
@@ -158,13 +178,6 @@ public class VideoWindow extends JFrame implements DeviceChangeListener {
 
     }
 
-    public void refreshDisplay() {
-        // TODO: Verify whether this is necessary. Does `repaint()' do anything if the window is not visible?
-        if (isVisible()) {
-            repaint();
-        }
-    }
-
     /**
      * Called by the CRTC on state change.
      */
@@ -239,15 +252,13 @@ public class VideoWindow extends JFrame implements DeviceChangeListener {
      * @param address The address of the character being requested.
      * @return An array of integers representing the pixel data.
      */
-    private int[] getGlyph(int address) {
-        int chr = videoRam[address];
+    private int[] getGlyph(int address) throws MemoryAccessException {
+        int chr = crtc.getCharAtAddress(address);
         int romOffset = (chr & 0xff) * (CHAR_HEIGHT * CHAR_WIDTH);
         int[] glyph = new int[CHAR_WIDTH * scanLinesPerRow];
 
         // Populate the character
-        for (int i = 0; i < (CHAR_WIDTH * Math.min(CHAR_HEIGHT, scanLinesPerRow)); i++) {
-            glyph[i] = charRom[romOffset + i];
-        }
+        arraycopy(charRom, romOffset, glyph, 0, CHAR_WIDTH * Math.min(CHAR_HEIGHT, scanLinesPerRow));
 
         // Overlay the cursor
         if (!hideCursor && crtc.isCursorEnabled() && crtc.getCursorPosition() == address) {
@@ -276,14 +287,17 @@ public class VideoWindow extends JFrame implements DeviceChangeListener {
      * Since the BufferedImage is a TYPE_BYTE_BINARY, the data must be converted
      * into a single byte per pixel, 0 for black and 255 for white.
 
-     * @param resource The ROM file resource to load.
      * @return An array of glyphs, each ready for insertion.
-     * @throws IOException
+     * @throws IOException Failure to load character ROM.
      */
-    private int[] loadCharRom(String resource) throws IOException {
-        BufferedInputStream bis = null;
-        try {
-            bis = new BufferedInputStream(this.getClass().getResourceAsStream(resource));
+    private int[] loadCharRom() throws IOException {
+        var resource = this.getClass().getResourceAsStream(ASCII_ROM);
+
+        if (resource == null) {
+            throw new IOException("Resource " + ASCII_ROM + " not found");
+        }
+
+        try (BufferedInputStream bis = new BufferedInputStream(resource)) {
             ByteArrayOutputStream bos = new ByteArrayOutputStream();
             while (bis.available() > 0) {
                 bos.write(bis.read());
@@ -298,7 +312,7 @@ public class VideoWindow extends JFrame implements DeviceChangeListener {
             int[] converted = new int[raw.length * CHAR_WIDTH];
 
             int romIndex = 0;
-            for (int i = 0; i < converted.length;) {
+            for (int i = 0; i < converted.length; ) {
                 byte charRow = raw[romIndex++];
 
                 for (int j = 7; j >= 0; j--) {
@@ -306,10 +320,6 @@ public class VideoWindow extends JFrame implements DeviceChangeListener {
                 }
             }
             return converted;
-        } finally {
-            if (bis != null) {
-                bis.close();
-            }
         }
     }
 }

src/main/java/com/loomcom/symon/ui/X11ResourceReader.java

@@ -0,0 +1,54 @@
+package com.loomcom.symon.ui;
+
+import com.sun.jna.Library;
+import com.sun.jna.Native;
+import com.sun.jna.Pointer;
+import com.sun.jna.ptr.IntByReference;
+import com.sun.jna.ptr.PointerByReference;
+import org.slf4j.Logger;
+import org.slf4j.LoggerFactory;
+
+public class X11ResourceReader {
+
+    private final static Logger logger = LoggerFactory.getLogger(X11ResourceReader.class.getName());
+
+
+    public interface X11 extends Library {
+        X11 INSTANCE = Native.load("X11", X11.class);
+
+        Pointer XOpenDisplay(String display);
+        Pointer XResourceManagerString(Pointer display);
+        void XCloseDisplay(Pointer display);
+    }
+
+    public static Double readXftDpiScale() {
+        Pointer display = null;
+        try {
+            display = X11.INSTANCE.XOpenDisplay(null);
+            if (display == null) {
+                return null; // não conseguimos ligar ao X server (ex: Wayland puro sem XWayland)
+            }
+
+            Pointer resourceString = X11.INSTANCE.XResourceManagerString(display);
+            if (resourceString == null) {
+                return null;
+            }
+
+            String resources = resourceString.getString(0);
+            for (String line : resources.split("\n")) {
+                if (line.startsWith("Xft.dpi:")) {
+                    int dpi = Integer.parseInt(line.split(":")[1].trim());
+                    return Math.round((dpi / 96.0) * 4) / 4.0;
+                }
+            }
+            return null;
+        } catch (UnsatisfiedLinkError | Exception e) {
+            logger.debug("Could not read X11 resource manager (libX11 unavailable?)", e);
+            return null;
+        } finally {
+            if (display != null) {
+                X11.INSTANCE.XCloseDisplay(display);
+            }
+        }
+    }
+}

src/main/java/com/loomcom/symon/util/FifoRingBuffer.java

@@ -1,5 +1,5 @@
 /*
- * Copyright (c) 2008-2013 Seth J. Morabito <sethm@loomcom.com>
+ * Copyright (c) 2008-2025 Seth J. Morabito <web@loomcom.com>
  *
  * Permission is hereby granted, free of charge, to any person obtaining
  * a copy of this software and associated documentation files (the
@@ -34,11 +34,11 @@ import java.util.Queue;
  */
 public class FifoRingBuffer<E> implements Iterable<E> {
 
-    private Queue<E> fifoBuffer;
-    private int maxLength;
+    private final Queue<E> fifoBuffer;
+    private final int maxLength;
 
     public FifoRingBuffer(int maxLength) {
-        this.fifoBuffer = new LinkedList<E>();
+        this.fifoBuffer = new LinkedList<>();
         this.maxLength = maxLength;
     }
 

src/main/java/com/loomcom/symon/util/Utils.java

@@ -1,5 +1,5 @@
 /*
- * Copyright (c) 2008-2013 Seth J. Morabito <sethm@loomcom.com>
+ * Copyright (c) 2008-2025 Seth J. Morabito <web@loomcom.com>
  *
  * Permission is hereby granted, free of charge, to any person obtaining
  * a copy of this software and associated documentation files (the
@@ -24,24 +24,9 @@
 package com.loomcom.symon.util;
 
 /**
- * Hex String Utilities.
- *
- * <p/>
- *
- * But why? Java, after all, has a number of ways to convert an integer into a hex string,
- * so it may look absurd to go to the trouble of writing yet another conversion! The answer is
- * performance.
- *
- * <p/>
- *
- * The most convenient way to get a formatted hex value from an integer is with the <code>String.format</code>
- * method, but this turns out to be extremely inefficient. Formatting a million integers
- * with <code>String.format</code> takes something like 1600ms. Formatting the same number of integers
- * with <code>HexUtil</code> takes only 160ms. This is on par with <code>Integer.toHexString</code>,
- * but also gives the desired padding.
- *
+ * Various Utilities
  */
-public class HexUtil {
+public class Utils {
 
     static final String NON_PRINTABLE = ".";
 
@@ -91,8 +76,19 @@ public class HexUtil {
                                            "F0", "F1", "F2", "F3", "F4", "F5", "F6", "F7",
                                            "F8", "F9", "FA", "FB", "FC", "FD", "FE", "FF"};
 
+    private static final String[] BIN_CONSTANTS = new String[256];
+
+    static {
+        for (int i = 0; i < 256; i++) {
+            String bin = Integer.toBinaryString(i);
+            // Left-pad to 8 digits with zeros
+            BIN_CONSTANTS[i] = "00000000".substring(bin.length()) + bin;
+        }
+    }
+
     /**
      * Very fast 8-bit int to ASCII conversion.
+     *
      * @param val The value of an ASCII character.
      * @return A string representing the ASCII character.
      */
@@ -121,9 +117,23 @@ public class HexUtil {
      * @return Four digit, zero padded hexadecimal string.
      */
     public static String wordToHex(int val) {
-        StringBuilder sb = new StringBuilder(4);
-        sb.append(HEX_CONSTANTS[(val >> 8) & 0xff]);
-        sb.append(HEX_CONSTANTS[val & 0xff]);
-        return sb.toString();
+        return HEX_CONSTANTS[(val >> 8) & 0xff] + HEX_CONSTANTS[val & 0xff];
+    }
+
+    /**
+     * Given two bytes, return an address.
+     */
+    public static int address(int lowByte, int hiByte) {
+        return ((hiByte << 8) | lowByte) & 0xffff;
+    }
+
+    /**
+     * Very fast 8-bit int to binary conversion, with zero-padded output.
+     *
+     * @param val The unsigned 8-bit value to convert to a zero padded binary string.
+     * @return Eight digit, zero padded binary string.
+     */
+    public static String byteToBin(int val) {
+        return BIN_CONSTANTS[val & 0xff];
     }
 }