8080-family hex vs. octal - was: 8080 Assembler-Text Editor (ATE)

Don Y dgy at DakotaCom.Net
Thu Apr 27 00:24:05 CDT 2006


Chuck Guzis wrote:
> Although I was well aware of the octal grouping of fields in the 8080, I
> adopted hex right off from the start, as I did when coding for the 8008.
> The problems dealing with "split" 16-bit quantites was too much of a hurdle
> to warrant octal.
> 
> As far as memorizing opcodes, that's neither here nor there.  While octal's
> nice for decoding moves, it's less of an issue for conditionals.  There's
> still a very recognizable pattern:
> 
> JNZ = C2
> JZ    = CA
> CNZ = C4
> CZ   = CC
> RNZ = C0
> RZ   =  C8
> 
> JNC = D2
> JC    = DA
> CNC = D4
> CC   = DC
> ...

Yes, there are similar "patterns" in most instructions
(e.g., LXI B/D/H/SP; INX B/D/H; PSH B/D/H; etc.).  But, in my
experience, you just memorized them because you always saw them
in certain combinations:

	PUSH AF
	PUSH BC
	PUSH DE
	PUSH HL

	...

	POP HL
	POP DE
	POP BC
	POP AF

	EI
	RETI

I can usually hand disassemble code faster than relying on
interactive / batch disassemblers (especially if you have
inline data and/or self-modifying code) just because these
patterns get to be *so* noticeable that you dont even bother
disassembling the code -- you just start writing the commentary
for the code!   (disassembling without adding commentary is
pretty useless)



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