[Coco] CoCo 3 MMU test for all
darccml at hotmail.com
Mon Jan 21 21:29:17 EST 2008
This looks like another situation that depends on the value of the last opcode byte fetched. The key thing to remember is that the last byte fetched isn't always the last byte of the current instruction, but may be the first byte of the next instruction.
Here are my test cases:
In this case, both B and location $600 end up containing $38. On the other hand...
results in both B and location $600 containing $F8. Furthermore...
results in both B and location $600 containing $78.
The critical ROM code for the PEEK command is:
This can also explain why PEEK returns $78, since the upper nybble of the JMP opcode is $7.
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