[Simh] ALTAIR thinko?

[Johnny Billquist]

Yeah, if you read the opcodes of the 8008, 8080 and Z80, you can easily 
see that it makes sense to actually read it in octal.

	Johnny

On 2015-02-03 03:09, Richard Cornwell wrote:
> All the books I have on the 8080 use Octal notation. Octal is great
> for the 8080 because the instruction encoding is based on a 2 bit field
> and 2 3 bit fields.
>
>    Opcodes with octal 0xx where special purpose operates, and rotate.
>                 octal 1ds  did moves between registers and memory.
>                 octal 2os  did operate with register and accumulator.
>                 octal 3xx  handled call/return and conditional jump.
>
> When the Z80 came out they started to use hex, and it made it more
> difficult to read the memory dump. I am not really sure why this change
> was made.
>
> Rich
>> On Mon, Feb 2, 2015 at 2:42 PM, Dell Setzer <dsetzer at panix.com> wrote:
>>
>>> Probably folks back then were used to octal from having worked on
>>> minicomputers (like DG or DEC).
>>
>>
>> I've forgotten that MIT's had grouped the switches in threes on their
>> panel like the PDP-8 and PDP-10, and PDP-11.  But you are right, that
>> was the way DEC had done it for years.
>>
>> ​So I think it depending where/hpw you grew up.   But you're right,
>> it if you came from the DEC world, you probably were used to using
>> octal from that 12 and 18 bit heritage. DEC did not really switch to
>> hex notation until the 32 bit Vax.  If your first assembly machines
>> was System 360 is the like, you probably learned hex.​
>>
>> Because I came up working on both DEC and IBM systems at the
>> beginning, I sort went both ways (was schizophrenic??).  When I wrote
>> C code (like drivers) I found I always prefered hex for bit
>> manipulations/masks in registers or results like CSRs or memory
>> reads, but since DEC published address in octal, assigned pointers in
>> octal - until the Vax.
>>
>> As for the micro's in those days, I tended to use hex exclusively in
>> assembler and C, since that's what Intel (or Moto or MOS Tech) had
>> defined in their architecture book.  In 1975, I could not afford a
>> MITs machine [I still have my copy of Pop 'tronics through) although
>> one of my friends got one for his birthday that summer with a whole
>> 256k bytes of memory [and I remember us drooling over it].  By late
>> '77 I did manage to score a KIM-1 with 1K of ram (which I still have)
>> -- FYI the KIM-1 it was purely hex.
>>
>> Clem
>
>
>


-- 
Johnny Billquist                  || "I'm on a bus
                                   ||  on a psychedelic trip
email: bqt at softjar.se             ||  Reading murder books
pdp is alive!                     ||  tryin' to stay hip" - B. Idol