8080 Assembler-Text Editor (ATE)

Don Y dgy at DakotaCom.Net
Mon Apr 17 20:21:07 CDT 2006

Dave Dunfield wrote:
>> When I was developing Z80-based products, an ongoing *battle*
>> was the use of hex vs. "split octal" (e.g., 0xFFFF -> 0377 0377).
>> The octal camp claimed the Z80 was an "octal machine" (oh, really?)
>> and, for "proof", showed how so many of the opcodes could be
>> committed to memory just my noting the source & destination
>> register "codes" and packing them into an octal representation:
>> xx xxx xxx  (of course, I wonder how well their argument would
>> stand up if Zilog had opted to encode the register fields
>> as:  xs dds dsx??  :> )
> 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).

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)

>> Octal?  Hex?  Just give me a symbolic debugger and let *it*
>> keep track of these minutae...
> By the time the Z80 was common, so were good assemblers and
> debuggers - but when the 8080 (ie: this instruction set) was designed,
> there was no such software commonly available for "personal use" -
> chances are your assembler was a pad of paper, a pencil and the Intel
> databook (thats how I wrote my earliest software). More often than not
> the debugger was a set of binary switches, or if you were really high-
> tech, a very simple poke into memory monitor squeezed into a 1702.

My first coding job was porting a 4004 based product to the 8080
(actually, the 8085 came out before we were done so that became
the target -- no real differences from the software standpoint)

> The only "symbolic" thing about it was the pad of paper (sometimes
> it was an integrated symbolic assembler/debugger, where you wrote
> out the code on one side of the pad, the hex opcodes in the middle
> and patches/debug notes on the right - of the same pad).
> Thats why a lot of people opted for Octal with the 8080 - in Octal
> the instruction set was fairly easy to remember ... For example
> '1sd' gave you all the MOV combinations. If you had the instruction
> set and it's encoding committed to memory, you could go a LOT
> faster during the "assembly phase". It also made debugging

Sure!  And for the 4004 we carried a small sheet of paper
neatly folded in half and tucked in our wallets.

> easier. I never got to like Octal, so I worked in hex anyway - I
> made "cheat sheets" to look up the opcodes, which I eventually
> memorized - I could go faster than most of the "Octal" guys...
>> Ah for the days of toggling in bootstrap loaders with front
>> panel switches.. :-/  (at least bigger machines treated octal
>> as "real" octal and not this "spilt octal" nonsense...)
> Agreed - one of the things I disliked most about Octal was the
> ambiguity over representation of 16-bit quantities, and the fact
> that you had to either "convert" to do it "right", or put up with a
> little 2/3 digit in the middle (which made mental arithmetic
> challenging) - The fact that you could just "stick two hex bytes
> together" was reason enough for me to keep with it.

Exactly.  Hence the advantage of things like the Nova over
the *80 devices -- you *know* you're dealing with words
instead of trying to cover both possibilities (with "split" octal).
I can still hear myself mumbling "High Low 377 377" (r.hl <- 0xFFFF)

> BTW - something I forgot to mention in my earlier post, Mits
> wasn't going against "Everyone else" - there were a number
> of other companies which embraced Octal for the 8080. Heath
> is another "biggie", but I saw a good chunk of other Octal based
> equipment during the time period.

More information about the cctalk mailing list