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Intersil 6100 PDP 8 Homebrew System

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  Intersil 6100 PDP 8 Homebrew System by Bill Degnan - 03/28/2013 23:40
Took a few photos of a homebrew Intersil 6100 PDP 8 Homebrew computer built by William F. Dudley Jr. which he donated to MARCH.


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I did not get a chance to photograph the ROM card (need to download the 2708 ROMs) nor the processor card. The front panel is a primitive four-digit octal dial. Here is a thread from Mid-Atlantic Retro message board:

William F. Dudley Jr. donated another wonderful box of homebrew parts to MARCH: a new unused Intersil 6100 eval kit, several PHI-deck digital cassettes (2 in the original blue eval cases), spare memory cards and schematics.
The intention was to build a PDP8
using the 6100 chips and the PHI decks
emulating DECtapes to run OS8 and all the PDP8 software.
Each memory card is 4k of 12 bit DRAM,
8 max per system.

They're all spare parts for the PDP8 he built.
That's the "mystery machine" from a few weeks ago,
so MARCH now has a homebrew PDP8!

Bill Dudley identified the "mystery machine" as his.
The flip-chip backplane was a clue
that it is DEC compatible!

> That's it. PDP-8 using the 6100 chip set.
>
> Oh, and the LEDs are actually HP dot matrix LEDs
> with builtin counter/decoder/driver/LED.
> Quite high-tech for 1976.
>
> If it's got that "flip-chip" bus, a baby blue front panel,
> thumb wheels, and those same memory cards, then that's it.

Later he added more info:
We'd need the following:
(to power system) 5v, +/-12v
serial terminal (ADM3A, TTY, etc)

and then, if it "works", you'd get a simple "ROM monitor" program that allows you to examine memory etc.

We implemented "extended memory" for our PDP-8, i.e. the ability to have up to 8 banks of 4K RAM. If you look at the actual hardware, you'll find three complete memory boards and one partially stuffed. That one is bank 7, which I *think* might have a monitor ROM burned into it.

> There are two 2708's on a card in the system. I was thinking it was a
> current loop set up, I can set the PC to the ROM address that I think
> is written on the chips, attach to a terminal (rs232 or current loop)
> and see what happens...come to the workshop if you want to do this with me.

It's not current loop, I built it to do RS232. That thumbwheel switch on the end of the ribbon cable is the baud rate selector: 110,150,300...9600 are the probable values.

Likely the reset button will cause execution to begin in the monitor.



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