Msg: 7062 *Conference*
04-04-97 18:36:28
From: RON WIESEN
To : COMET _
Subj: REPLY TO MSG #5319 (UNDOCUMENTED 80C85 OPCODES)
Using DBG in either ROM2 or developer ROM2 there is: (1) an op-code unknown by disassembly, and (2) an op-code that disassembles differently based on state of ROM switch (standard ROM or option ROM). In the case of both of these op-codes, the ROM or RAM locale of the op-code byte (<8000h for ROM or =>8000h for RAM) is not a factor in disassembly. Op-code CBh disassembles as ?? memadr Op-code CFh disassembles as: RST 1 - switch on standard ROM CSR memadr - switch on option ROM Now if I could only remember the op-code you inquired about for RST V. Was it CBh? Yes, it was. So op-code CBh has no mnemonic from ROM2's disassembly - other than "??". But now I pose another mystery: what is ROM2's meaning of the "CSR" mnemonic, and why does ROM2 give it (versus RST 1) when ROM2 knowns the option ROM (itself) is selected. Maybe it's a clue to a variance of action in the Model T by the RST 1 instruction - doubtful. Guess I best get my RELOC1.BA and doc files from the Upload area and review the op-codes I added. If CBh is one of them, I'll be surprised. Later Comet, and a mighty "Hail Comet" - I mean Hale-Bopp.