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 <[email protected]> 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: [email protected] || Reading murder books
pdp is alive! || tryin' to stay hip" - B. Idol
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