CPU bug fixes and Simulator enhancements.
Bug Fixes: - Fixed several bugs in the CPU that caused processor status flags to be set incorrectly. Instructions affected were: STA, STX, STY, CMP, CPX, CPY, BIT. - Made some internal-use-only methods on the CPU class private. - Fixed incorrect disassembly of (Indirect,X) and (Indirect),Y instructions. Although this didn't affect behavior, it certainly caused me some confusion in debugging. - Added missing "BCS" instruction to instruction table. Enhancements: - Now includes a full version of Lee Davison's Enhanced 6502 BASIC bundled as source code and a ROM image. Get that REAL COMPUTER EXPERIENCE!(tm) - If a file named "rom.bin" exists in the same directory where the simulator is executed, it will be loaded at addresses $d000-$ffff. - Gave the CPU an idle loop to make simulated timing a little more realistic (but this is still an area needing major improvement) - Changed the CPU's toString() method to give better debugging output. - Added a small typeahead buffer to the Console. - Better exception messaging. Misc: - Bumped version to 0.5, updated README.
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*.rom
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*.lst
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*.map
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*.o
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CA=ca65
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LD=ld65
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all: ehbasic
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ehbasic: ehbasic.o
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$(LD) -C symon.config -vm -m ehbasic.map -o ehbasic.rom ehbasic.o
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ehbasic.o:
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$(CA) --listing -o ehbasic.o min_mon.asm
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clean:
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rm -f *.o *.rom *.map *.lst
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This directoy contains a very slightly modified version of EhBASIC 2.22
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to support the Symon simulator.
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Usage
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-----
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The pre-assemled ROM image 'ehbasic.rom' in the "samples" directory is all you
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need unless you want to rebuild this source code.
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Just copy the image 'ehbasic.rom' to the directory where you run Symon, and
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rename the file to 'rom.bin'. It will be loaded at memory location $D000 when
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the simulator starts up. Click "Run" and you'll be presented with BASIC.
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At the first prompt, type 'C' for a Cold Start
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When prompted for free memory, type: $C000
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Note that EhBASIC only accepts upper case input, so you'll need to use caps
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lock (the cruise control for cool) to really make the most of it.
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Building
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--------
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To build it, you'll need the CC65 tool chain from http://www.cc65.org/
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and a suitable version of 'make'. Just typing:
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% make
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in this directory should re-build everything. You'll get a listing,
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some object files, and the ROM image itself.
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Changes from the EhBASIC 2.22
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-----------------------------
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- Minor syntax changes to allow assembly with the cc65 tool chain.
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- Memory map modified for Symon.
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- At reset, configure the 6551 ACIA for 8-N-1, 2400 baud.
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- Monitor routines 'ACIAin' and 'ACIAout' modified for the 6551 ACIA.
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Specifically, reading and writing will check the 6551 status register for
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the status of rx and tx registers before receive or transmit.
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EhBASIC is copyright Lee Davison <leeedavison@googlemail.com>
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My changes are so slight that I hesitate to even say this, but for "CYA"
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reasons:
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Changes are copyright Seth Morabito <web@loomcom.com> and are distributed under
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the same license as EhBASIC. I claim no commercial interest whatsoever. Any
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commercial use must be negotiated directly with Lee Davison.
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Original EhBASIC 2.22 README
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----------------------------
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Enhanced BASIC is a BASIC interpreter for the 6502 family microprocessors. It
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is constructed to be quick and powerful and easily ported between 6502 systems.
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It requires few resources to run and includes instructions to facilitate easy
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low level handling of hardware devices. It also retains most of the powerful
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high level instructions from similar BASICs.
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EhBASIC is free but not copyright free. For non commercial use there is only one
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restriction, any derivative work should include, in any binary image distributed,
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the string "Derived from EhBASIC" and in any distribution that includes human
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readable files a file that includes the above string in a human readable form
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e.g. not as a comment in an HTML file.
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For commercial use please contact me, Lee Davison, at leeedavison@googlemail.com
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for conditions.
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For more information on EhBASIC, other versions of EhBASIC and other projects
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please visit my site at ..
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http://mycorner.no-ip.org/index.html
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P.S. c't magazin, henceforth refered to as "those thieving german bastards", are
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prohibited from using this or any version of EhBASIC for any of their projects
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or products. The excuse "we don't charge people for it" doesn't wash, it adds
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value to your product so you owe me.
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File diff suppressed because it is too large.
Load diff
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; minimal monitor for EhBASIC and 6502 simulator V1.05
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; To run EhBASIC on the simulator load and assemble [F7] this file, start the simulator
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; running [F6] then start the code with the RESET [CTRL][SHIFT]R. Just selecting RUN
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; will do nothing, you'll still have to do a reset to run the code.
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.feature labels_without_colons
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.include "basic.asm"
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; put the IRQ and MNI code in RAM so that it can be changed
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IRQ_vec = VEC_SV+2 ; IRQ code vector
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NMI_vec = IRQ_vec+$0A ; NMI code vector
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; setup for the 6502 simulator environment
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IO_AREA = $C000
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ACIAdata = IO_AREA ; simulated ACIA r/w port
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ACIAstatus = IO_AREA+1
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ACIAcommand = IO_AREA+2
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ACIAcontrol = IO_AREA+3
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; now the code. all this does is set up the vectors and interrupt code
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; and wait for the user to select [C]old or [W]arm start. nothing else
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; fits in less than 128 bytes
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.segment "MONITOR"
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.org $FF00 ; pretend this is in a 1/8K ROM
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; reset vector points here
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RES_vec
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CLD ; clear decimal mode
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LDX #$FF ; empty stack
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TXS ; set the stack
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; Initialize the ACIA
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ACIA_init
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LDA #$09
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STA ACIAcommand
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LDA #$1A ; Set output for 8-N-1 2400
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STA ACIAcontrol
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; set up vectors and interrupt code, copy them to page 2
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LDY #END_CODE-LAB_vec ; set index/count
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LAB_stlp
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LDA LAB_vec-1,Y ; get byte from interrupt code
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STA VEC_IN-1,Y ; save to RAM
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DEY ; decrement index/count
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BNE LAB_stlp ; loop if more to do
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; now do the signon message, Y = $00 here
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LAB_signon
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LDA LAB_mess,Y ; get byte from sign on message
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BEQ LAB_nokey ; exit loop if done
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JSR V_OUTP ; output character
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INY ; increment index
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BNE LAB_signon ; loop, branch always
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LAB_nokey
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JSR V_INPT ; call scan input device
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BCC LAB_nokey ; loop if no key
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AND #$DF ; mask xx0x xxxx, ensure upper case
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CMP #'W' ; compare with [W]arm start
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BEQ LAB_dowarm ; branch if [W]arm start
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CMP #'C' ; compare with [C]old start
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BNE RES_vec ; loop if not [C]old start
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JMP LAB_COLD ; do EhBASIC cold start
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LAB_dowarm
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JMP LAB_WARM ; do EhBASIC warm start
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; byte out to simulated ACIA
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ACIAout
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PHA ; save accumulator
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ACIAout_w
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LDA ACIAstatus ; Read 6551 status
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AND #$10 ; Is tx buffer full?
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BEQ ACIAout_w ; if not, loop back
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PLA ; Otherwise, restore accumulator
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STA ACIAdata ; write byte to 6551
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RTS
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; byte in from simulated ACIA
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ACIAin
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LDA ACIAstatus ; Read 6551 status
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AND #$08 ;
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BEQ LAB_nobyw ; If rx buffer empty, no byte
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LDA ACIAdata ; Read byte from 6551
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SEC ; Flag byte received
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RTS
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LAB_nobyw
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CLC ; flag no byte received
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no_load ; empty load vector for EhBASIC
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no_save ; empty save vector for EhBASIC
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RTS
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; vector tables
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LAB_vec
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.word ACIAin ; byte in from simulated ACIA
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.word ACIAout ; byte out to simulated ACIA
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.word no_load ; null load vector for EhBASIC
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.word no_save ; null save vector for EhBASIC
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; EhBASIC IRQ support
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IRQ_CODE
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PHA ; save A
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LDA IrqBase ; get the IRQ flag byte
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LSR ; shift the set b7 to b6, and on down ...
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ORA IrqBase ; OR the original back in
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STA IrqBase ; save the new IRQ flag byte
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PLA ; restore A
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RTI
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; EhBASIC NMI support
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NMI_CODE
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PHA ; save A
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LDA NmiBase ; get the NMI flag byte
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LSR ; shift the set b7 to b6, and on down ...
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ORA NmiBase ; OR the original back in
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STA NmiBase ; save the new NMI flag byte
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PLA ; restore A
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RTI
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END_CODE
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LAB_mess
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.byte $0D,$0A,"6502 EhBASIC [C]old/[W]arm ?",$00
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; sign on string
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; system vectors
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.segment "VECTORS"
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.org $FFFA
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.word 0 ; NMI vector
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.word RES_vec ; RESET vector
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.word 0 ; IRQ vector
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MEMORY {
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RAM1: start = $0000, size = $C000;
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ROM1: start = $D000, size = $2F00, fill = yes;
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MONITOR: start = $FF00, size = $FA, fill = yes;
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ROMV: start = $FFFA, size = $6, file = %O, fill = yes;
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}
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SEGMENTS {
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CODE: load = ROM1, type = ro;
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DATA: load = ROM1, type = ro;
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MONITOR: load = MONITOR, type = ro;
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VECTORS: load = ROMV, type = ro;
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}
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SYMBOLS {
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__STACKSIZE__ = $0300;
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}
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