Michael A. Terrell
Did you ever use the 6510 processor? It was a 6502 with an
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onboard I?O port that was made foe the Commodore 64. There were several
undocumented opcodes thet were different on different production runs.
Some commercial software would only run on a specific group, so I fad to
keep as many different runs on hand, as possible to get someone's sytem
back up and running. Also: Did any of you work with Motorola's 6800 based
Exorcisor bus? I had to maintain a pair of six NTSC output character
generators built with those boards. Each video output had its own card, but
each computer only had 32KB of RAM.
On Mon, Jan 20, 2020 at 1:21 PM Harvey White <madyn@...> wrote:
I (very early on) tried to build a Tektronix calculator out of TTL,
jumps, program flow, and then an FPU.
Got the jumps and program flow working, you could do an indirect jump
through a location in hardware (and yes, this was very early....)
I built an 8 trace scope switch to be able to look at digital traces on
my 513D (I got lucky getting the 513D, P11 phosphor).
Simple enough, sync a counter to the sweep trigger output, take the
counter, run it to a multiplexer and weight the multiplexer output as
'1' in a very crude D/A.
Take the appropriate counter outputs and weight them 2, 4 and 8.
Instant 8 traces on a 1 channel scope, for 5 volt TTL, of course.
Then along came the 6502, for 30 dollars, one each (while the 8080 was
still 100 dollars or so). I looked at my 130 chip wirewrapped design
(still not done), and felt a bit bad.......
I bought two (and literally, drove to the MOS technology factory to pick
them up with the original books). Still have them, I think.
There were some bugs in the microcode, some things not implemented, and
I seem to remember being bitten by that once I got the "newer" processors.
Naturally, the whole thing was in assembly language. Program the thing
at work (someone tweaked the DG macro assembler), program the UVPROMS,
take it home and single step (hardware) through the program.
Everything was wirewrap then. Just everything.
On 1/20/2020 9:39 AM, Chuck Harris wrote:
Many of us early adopters to microprocessors got bit byup line to a HP2000 at the Stanford business school using DECWriters, and
the discovery that not all of the 8080's made were truly
Everyone knows that Intel developed the 8080, but some might
not remember that the Japanese company NEC, almost immediately
introduced a cheaper, unauthorized, second source to the 8080...
only theirs was partly done from Intel's design, and partly
done on their own.
Some of the subtle differences were in the settings of flags
after some arithmetic operations, and in the numbers of clock
cycles used by some common instructions.
I discovered the flag problem, when I found some code that
should have branched, only it didn't... NEC fixed a mistake in
the Intel microcode.
I discovered the clock cycle problem when I was writing a music
program, that played on a transistor radio... using timing loops.
I meticulously counted cycles, ala the Intel data book, but
several notes were coming out sharp.
It turns out that Intel used 5 cycles for one instruction, and
NEC found a way to do it in 4 cycles...
And, I had stacks of these instructions, inside of loops that
timed the note pitch.
Dave Seiter wrote:
Grin! Things were different back then. In high school we had dial
one could wander through the directories, browsing students projects. It
was usually very responsive, but sometimes it would really bog down, and
we'd have to use one of the in-class micros (PET/APPLEII/TRS80) to work on
our projects. But they were all more reliable than our PDP8/E; we had to
use that for Fortran, and it was always breaking down. I think I was one
of the last people to learn how to use a keypunch machine!