[Simh] ALTAIR thinko?

[Richard Cornwell]

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



-- 
==========================================================================
Richard Cornwell
skyvis at sky-visions.com
http://sky-visions.com
==========================================================================