8080 Assembler-Text Editor (ATE)
dave06a at dunfield.com
Tue Apr 18 07:01:00 CDT 2006
> > I'm not promoting the Octal side (indeed I much prefer HEX), however
> > Zilog didn't "opt" for anything - they based their design and instruction
> > set decoding on the Intel 8080, which was laid out in a manner which
> > made sense with "Octal". And Intel DIDN'T use xsddsdsx, they DID use
> > xxdddsss - which made perfect sense from an Octal standpoint (which
> > is why so many people promoted the use of Octal with it).
> But the Z80 isn't an 8085 nor is the 8085 an 8080. (granted, the
> last two are much closer related than the first two).
But the Z80 and the 8085 are both based on the 8080 architecture
and instruction set - so much so that they will both run the vast
majority of 8080 code. Is anyone really suggesting that it's an
"accident" that the Z80 happens to run 8080 code ... or did
Zilog begin with the 8080 instruction set definition (hence my point
that they (Zilog) did not make the decision on the bit arrangements
of the opcoodes).
> And, there is no reason why xx ddd sss is any *better* than
> xs dsd sdx or sd xxd ssd for an instruction encoding. *We*
> used (split) octal because our MTOS supported hot patching
> and it was convenient to "hand assemble" code patches on the
> fly to fix bugs, etc. (gdb wasn't around for an 8080 in ~1976)
Doesn't this suggest that xxdddsss actually was *better* - since
you took advantage of the alignment with octal notation to make it
easier to hand-assemble...
Thats my whole point. The fact that the instruction set happens to
align well with Octal notation is the main reason that a lot of people
used it. It's interesting to note that almost all of the Intel docs are
in hex, or binary notations - but Mits, Heath and several others
thought that Octal was a better fit.
As noted earlier, I happen to be from the "hex" camp ... but I don't
think it's fair to dismiss the octal guys as "nuts" ... the use of octal
on the 8080 did have some benefit, and there were a lot of people
who went that route - to ignore or discount this does not present an
accurate depiction of the time period.
Now why some people chose octal for other processors, which
didn't have an architectural slant toward 8 is more of a mystery
dave06a (at) Dave Dunfield
dunfield (dot) Firmware development services & tools: www.dunfield.com
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