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ID Category [?] Severity [?] Reproducibility Date Submitted Last Update
06798 Core Critical (emulation) Always Dec 24, 2017, 07:27 Dec 24, 2017, 11:38
Tester drencorxeen View Status Public Platform MAME (Official Binary)
Assigned To Resolution Duplicate OS Windows 10 (64-bit)
Status [?] Closed Driver coco3.cpp
Version 0.192 Fixed in Version Build 64-bit
Summary MESS-specific 06798: m6809 incorrectly handling opcode 0x104F
Description On a real m6809 CPU if you run a opcode of 0x104F the real 6809 will ignore the 0x10 opcode part of the instruction and will process the opcode of 0x4F which on a m6809 is a CLRA.

Please test on coco3, coco1, coco2.
Steps To Reproduce Created a test assembly language program to load register D with $FFFF, then issue a 6309 instruction CLRD, then after that writing register A and register B to specific memory locations and using basic to peek and print the values should yield a 0 for A and 255 for B, but the m6809 core in MAME ignores both bytes of the CLRD where it should have only ignored the 0x10.

I am including a DSK image for testing.

Steps once disk image is mounted in drive 0:

On real CoCo 1, 2, 3 with a real m6809 in it the outputs as follows:

On emulator outputs:
Additional Information So the 6309 instruction CLRD (0x104F) the (0x10) is ignored on a real m6809 CPU and thus it still processes the (0x4F) part of the instruction and does a CLRA.

I have tested this on a system that does in fact have a real m6809 on it and thus I know in this case how the emulation for the m6809 is not handling this situation correctly.
Regression Version
Affected Sets / Systems
Attached Files
zip file icon (695 bytes) Dec 24, 2017, 07:27 Uploaded by drencorxeen
duplicate of 06797Acknowledged MC6809 incorrectly handling opcode 0x104F 
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