PDP-8 micro, circa 1976
Christian Doucet
To what's-his-name-who-asked-what-was-the-machine-using-a-PDP-8-chip:
Just thumbed through the DDJ (V1N7) I used yesterday to quote the cover
and I stumbled (to my upmost surprise) on an article on the
mystery (sp?) machine using an Intersil IM-6100 (the PDP-8 on a chip).
It was called the PCM-12, and its cpu emulated a PDP-8/E (except the
i/o instructions).
The company making it was called (oh, surprise) `PCM', and was located
at: box 215, San Ramon CA 94583.
system with 1K word RAM: $799 (kit) or $1224 (assembled)
to expand to 4K: another $139 (kit)
...
`complete' system (8K of 12 bit words, in kit form): $1415
Bruno Majewski
Frank Zsitvay
>Greeting,
>
>To what's-his-name-who-asked-what-was-the-machine-using-a-PDP-8-chip:
>
>Just thumbed through the DDJ (V1N7) I used yesterday to quote the cover
>and I stumbled (to my upmost surprise) on an article on the
>mystery (sp?) machine using an Intersil IM-6100 (the PDP-8 on a chip).
>
>It was called the PCM-12, and its cpu emulated a PDP-8/E (except the
>i/o instructions).
>
intersil IM6100. since the 6100 couldn't generate a microprocessor
bus on its own, they also used a Z80 on the same board. I never saw
any software for this board, and I am not sure how many were ever sold,
but i did see one.
What struck me as particularly strange about the pdp-8 architecture
was the way memory was organized and the way subroutines were handled.
It made sense if you had core memory available, but using modern RAMS
and EPROMS you would have a serious problem getting the thing to work.
most notably, subroutines in ROM would need to build a 'jump table'
in RAM during setup and have all references made in the jump table since
the PDP-8 puts the return address into the first word of the routine
itself. (or use an exception latch...)
since the PDP-8 could access 4K of 12-bit words, Intersil provided
a paged memory chip which would allow you to bank switch in a total
of 96K words into the memory space of the processor, but each one was
a separate, distinct chunk of memory, and moving data between them was
a real mess.
but the thing was definately a representation of computing philosophy
of the late 60s/early 70s...
I wonder how many systems with 6100 CPUs were ever sold...
--
fzsi...@techbook.COM - but don't quote me on that....
According to a reputable source, 'glastnost' translated from Russian
really means 'lesser grade of barbed wire.'
Michael Ardai
- Ohio Scientific made a board for their machines that also used the
-intersil IM6100. since the 6100 couldn't generate a microprocessor
-bus on its own, they also used a Z80 on the same board. I never saw
-any software for this board, and I am not sure how many were ever sold,
-but i did see one.
Maybe they did make one, but their triple CPU board (for the 8P, I think)
used the 6502, Z80, and 6800, not the 6100.
/mike
--
\|/ Michael L. Ardai N1IST (617) 254-3420
--- -------------------------------------------------------------------------
/|\ ar...@teda.teradyne.com ar...@bu-pub.bu.edu Teradyne EDA East
Joe Pollock
>was the way memory was organized and the way subroutines were handled.
>It made sense if you had core memory available, but using modern RAMS
>and EPROMS you would have a serious problem getting the thing to work.
>most notably, subroutines in ROM would need to build a 'jump table'
>in RAM during setup and have all references made in the jump table since
>the PDP-8 puts the return address into the first word of the routine
>itself. (or use an exception latch...)
>
> since the PDP-8 could access 4K of 12-bit words, Intersil provided
>a paged memory chip which would allow you to bank switch in a total
>of 96K words into the memory space of the processor, but each one was
>a separate, distinct chunk of memory, and moving data between them was
>a real mess.
>
> but the thing was definately a representation of computing philosophy
>of the late 60s/early 70s...
>
> I wonder how many systems with 6100 CPUs were ever sold...
>
>--
>fzsi...@techbook.COM - but don't quote me on that....
>
The PDP-8I and PDP-8E were popular enough to attract a number of third-
party hardware vendors. In particular, I recall an add-in memory system for
the 8/E (I think I got it right that time) that was in use at the university
where I performed hardware maintenance. Anyway, instead of using something
reasonable, like a clock generator or delay line, this memory system used a
number of SN74121 multivibrator chips, each with its own trimpots. We never
could get that memory set up in a reliable manner. Lacking a frequency counter
with better than 100 ns single-pulse-width resolution didn't help :-) Anyway,
that was an attempt to use 2K BIT memory chips to substitute directly for a
core memory system (as I recall, the system plugged into the system memory
bus - it's been a _long_time). We also decided that it would be a good idea
for the psychologists to check with the engineering/maintenance people before
purchasing hardware :-)
Wasn't the 6100 chip also used in the Decmate word processor system?
I know the PDP-8 cpu was; does any DEC employee recall the source of the
chip set? I have one of the Intel protoboards for this system, speaking
of nostalgia...
Joe Pollock
The Evergreen State College
Olympia WA 98505 pol...@milton.u.washington.edu
"I never throw anything out..."
C
The PDP-8