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.