🚀 go-pugleaf

On Mon, 23 Jul 2018 12:16:48 +0100, Brian Reay wrote:

> In the mid/late 70s, when I was at Uni, I had a vacation job and worked
> on a project involving the 6100 uP.
> 
> Initially, I was let loose on a simple singe board dev system (if you
> can call it that), a simple keyboard, 7 segment display etc, as was
> common at the time.
> 
> Eventually, I was trusted to use a 'real computer' - laughable by
> today's standards but ..... . It was a typical (at the time) 'Pizza Box'
> 6100 based unit, I'm pretty sure it had toggle switches for data and
> address set up etc but I used other machines around then and it was 40
> years ago, the usual LEDs etc. I/O was teletype etc.- no CRT etc.  I'm
> sure at the time, Intersil were the only make of the 6100 and probably
> made the Pizza Box.
> 
> Purely for old times sake, I'd like to try and acquire one- if the price
> is right.
> 
> Does anyone know the beast, please?

Yes, I do. Or, rather I have two of the 'second source' version, from 
Harris. The 6120, in fact, which was slightly enhanced.

You may know that the instruction set was that of the Digital Equipment 
Corp. PDP-8; a nice little, very successful minicomputer first announced 
on 28th May 1965. That used discrete logic, then later SSI TTL logic. 
They ended up with the 6100/6120.

I have built two kits using the 6120, but I obtained the actual CPU chips 
as part of the kits, from someone who had acquired a limited supply. The 
kits are no longer available.

Here are both versions:

  http://www.bobeager.uk/projects.html#sbc6120

The panel is a near replica on an early model of the PDP-8.

You can't get the chip, but there is a PDP-8 simulator available for most 
platforms, which simulates the entire instruction set. Even better, there 
is a kit available (the PiDP-8) which is a scale model (physically) of a 
later version of the PDP-8. I have the kit, but no tuit yet!

 http://obsolescence.wixsite.com/obsolescence/pidp-8

Lots of software and resources available for the 6100/6120/PDP-8.

There is also a PiDP-11...I have that too.

The PDP-8 architecture is very simple. 12 bit word, with a 3 bit opcode 
field (i.e. 8 instructions!). TAD (add), DCA (store and clear 
accumulator), AND, JMP, JMS (subroutine call), ISZ (increment and skip if 
zero). Then an I/O group (IOT) and the operate group (instructions not 
needing an address).

The other 9 bits were a 7 bit address, a bit for indirection, and a bit 
setting the address 'page' (128 word block), either the current one of 
the zeroth one (rather like the 6502 years later).

The operate group used the address bits to specify microcoded actions.

Many resources, but here's an example.

 http://homepage.divms.uiowa.edu/~jones/pdp8/man/index.html
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