diff --git a/src/main/java/com/loomcom/symon/devices/Acia6850.java b/src/main/java/com/loomcom/symon/devices/Acia6850.java
index bd70eed..e957bb4 100644
--- a/src/main/java/com/loomcom/symon/devices/Acia6850.java
+++ b/src/main/java/com/loomcom/symon/devices/Acia6850.java
@@ -30,8 +30,8 @@ import com.loomcom.symon.exceptions.MemoryRangeException;
 
 /**
  * This is a simulation of the Motorola 6850 ACIA, with limited
- * functionality.  Interrupts are not supported.
- * <p/>
+ * functionality.
+ *
  * 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
@@ -56,9 +56,6 @@ public class Acia6850 extends Acia {
     public int read(int address, boolean cpuAccess) throws MemoryAccessException {
         switch (address) {
             case RX_REG:
-                if (cpuAccess) {
-                    interrupt = false;
-                }
                 return rxRead(cpuAccess);
             case STAT_REG:
                 return statusReg(cpuAccess);
@@ -72,9 +69,6 @@ public class Acia6850 extends Acia {
     public void write(int address, int data) throws MemoryAccessException {
         switch (address) {
             case TX_REG:
-                if (cpuAccess) {
-                    interrupt = false;
-                }
                 txWrite(data);
                 break;
             case CTRL_REG:
@@ -119,6 +113,10 @@ public class Acia6850 extends Acia {
             stat |= 0x80;
         }
 
+        if (cpuAccess) {
+            interrupt = false;
+        }
+
         return stat;
     }
 
diff --git a/src/test/java/com/loomcom/symon/AciaTest6850.java b/src/test/java/com/loomcom/symon/Acia6850Test.java
similarity index 63%
rename from src/test/java/com/loomcom/symon/AciaTest6850.java
rename to src/test/java/com/loomcom/symon/Acia6850Test.java
index 0f7425c..e37539d 100644
--- a/src/test/java/com/loomcom/symon/AciaTest6850.java
+++ b/src/test/java/com/loomcom/symon/Acia6850Test.java
@@ -7,7 +7,7 @@ import org.junit.Test;
 import static org.junit.Assert.assertEquals;
 import static org.mockito.Mockito.*;
 
-public class AciaTest6850 {
+public class Acia6850Test {
     
     private final static int CMD_STAT_REG = 0;
     private final static int DATA_REG = 1;
@@ -91,6 +91,78 @@ public class AciaTest6850 {
         verify(mockBus, never()).assertIrq();
     }
 
+    @Test
+    public void shouldTriggerInterruptFlagOnRxFullIfRxIrqEnabled() throws Exception {
+        Bus mockBus = mock(Bus.class);
+
+        Acia acia = newAcia();
+        acia.setBus(mockBus);
+
+        // Disable TX IRQ, Enable RX IRQ
+        acia.write(CMD_STAT_REG, 0x80);
+
+        acia.rxWrite('a');
+
+        // Receive should cause IRQ flag to be set
+        assertEquals(0x80, acia.read(0x0000, true) & 0x80);
+    }
+
+    @Test
+    public void shouldNotTriggerInterruptFlagOnRxFullIfRxIrqNotEnabled() throws Exception {
+        Bus mockBus = mock(Bus.class);
+
+        Acia acia = newAcia();
+        acia.setBus(mockBus);
+
+        // Disable TX IRQ, Disable RX IRQ
+        acia.write(CMD_STAT_REG, 0x00);
+
+        acia.rxWrite('a');
+
+        // Receive should not cause IRQ flag to be set
+        assertEquals(0x00, acia.read(0x0000, true) & 0x80);
+    }
+
+    @Test
+    public void shouldTriggerInterruptFlagOnTxEmptyIfTxIrqEnabled() throws Exception {
+        Bus mockBus = mock(Bus.class);
+
+        Acia acia = newAcia();
+        acia.setBus(mockBus);
+
+        // Enable TX IRQ, Disable RX IRQ
+        acia.write(CMD_STAT_REG, 0x20);
+
+        // Write data
+        acia.write(1, 'a');
+
+        verify(mockBus, never()).assertIrq();
+
+        // Transmission should cause IRQ flag to be set
+        acia.txRead(true);
+
+        assertEquals(0x80, acia.read(0x0000, true) & 0x80);
+    }
+
+    @Test
+    public void shouldNotTriggerInterruptFlagOnTxEmptyIfTxIrqNotEnabled() throws Exception {
+        Bus mockBus = mock(Bus.class);
+
+        Acia acia = newAcia();
+        acia.setBus(mockBus);
+
+        // Disable TX IRQ, Disable RX IRQ
+        acia.write(CMD_STAT_REG, 0x02);
+
+        // Write data
+        acia.write(DATA_REG, 'a');
+
+        // Transmission should not cause IRQ flag to be set
+        acia.txRead(true);
+
+        assertEquals(0x00, acia.read(0x0000, true) & 0x80);
+    }
+
     @Test
     public void newAciaShouldHaveTxEmptyStatus() throws Exception {
         Acia acia = newAcia();
@@ -129,6 +201,24 @@ public class AciaTest6850 {
     @Test
     public void aciaShouldOverrunAndReadShouldReset()
             throws Exception {
+
+        Acia acia = newAcia();
+
+        // overrun ACIA
+        acia.rxWrite('a');
+        acia.rxWrite('b');
+
+        assertEquals(0x20, acia.read(CMD_STAT_REG, true) & 0x20);
+
+        // read should reset
+        acia.rxRead(true);
+        assertEquals(0x00, acia.read(CMD_STAT_REG, true) & 0x20);
+
+    }
+
+    @Test
+    public void aciaShouldOverrunAndMemoryWindowReadShouldNotReset()
+            throws Exception {
         
         Acia acia = newAcia();
         
@@ -138,9 +228,9 @@ public class AciaTest6850 {
         
         assertEquals(0x20, acia.read(CMD_STAT_REG, true) & 0x20);
         
-        // read should reset
-        acia.rxRead(true);
-        assertEquals(0x00, acia.read(CMD_STAT_REG, true) & 0x20);
+        // memory window read should not reset
+        acia.rxRead(false);
+        assertEquals(0x20, acia.read(CMD_STAT_REG, true) & 0x20);
         
     }
 
diff --git a/src/test/java/com/loomcom/symon/AciaTest.java b/src/test/java/com/loomcom/symon/AciaTest.java
index 4e5bb1f..ba29b27 100644
--- a/src/test/java/com/loomcom/symon/AciaTest.java
+++ b/src/test/java/com/loomcom/symon/AciaTest.java
@@ -73,12 +73,84 @@ public class AciaTest {
         // Write data
         acia.write(0, 'a');
 
-        // Transmission should cause IRQ
+        // Transmission should not cause IRQ
         acia.txRead(true);
 
         verify(mockBus, never()).assertIrq();
     }
 
+    @Test
+    public void shouldTriggerInterruptFlagOnRxFullIfRxIrqEnabled() throws Exception {
+        Bus mockBus = mock(Bus.class);
+
+        Acia acia = new Acia6551(0x000);
+        acia.setBus(mockBus);
+
+        // Disable TX IRQ, Enable RX IRQ
+        acia.write(2, 0x00);
+
+        acia.rxWrite('a');
+
+        // Receive should cause IRQ flag to be set
+        assertEquals(0x80, acia.read(0x0001, true) & 0x80);
+    }
+
+    @Test
+    public void shouldNotTriggerInterruptFlagOnRxFullIfRxIrqNotEnabled() throws Exception {
+        Bus mockBus = mock(Bus.class);
+
+        Acia acia = new Acia6551(0x000);
+        acia.setBus(mockBus);
+
+        // Disable TX IRQ, Disable RX IRQ
+        acia.write(2, 0x02);
+
+        acia.rxWrite('a');
+
+        // Receive should not cause IRQ flag to be set
+        assertEquals(0x00, acia.read(0x0001, true) & 0x80);
+    }
+
+    @Test
+    public void shouldTriggerInterruptFlagOnTxEmptyIfTxIrqEnabled() throws Exception {
+        Bus mockBus = mock(Bus.class);
+
+        Acia acia = new Acia6551(0x000);
+        acia.setBus(mockBus);
+
+        // Enable TX IRQ, Disable RX IRQ
+        acia.write(2, 0x06);
+
+        // Write data
+        acia.write(0, 'a');
+
+        verify(mockBus, never()).assertIrq();
+
+        // Transmission should cause IRQ flag to be set
+        acia.txRead(true);
+
+        assertEquals(0x80, acia.read(0x0001, true) & 0x80);
+    }
+
+    @Test
+    public void shouldNotTriggerInterruptFlagOnTxEmptyIfTxIrqNotEnabled() throws Exception {
+        Bus mockBus = mock(Bus.class);
+
+        Acia acia = new Acia6551(0x000);
+        acia.setBus(mockBus);
+
+        // Disable TX IRQ, Disable RX IRQ
+        acia.write(2, 0x02);
+
+        // Write data
+        acia.write(0, 'a');
+
+        // Transmission should not cause IRQ flag to be set
+        acia.txRead(true);
+
+        assertEquals(0x00, acia.read(0x0001, true) & 0x80);
+    }
+
     @Test
     public void newAciaShouldHaveTxEmptyStatus() throws Exception {
         Acia acia = new Acia6551(0x000);