Fabritek MP-12 Loader

[Kyle Owen]

On Thu, Dec 3, 2015 at 2:24 PM, Josh Dersch <derschjo at gmail.com> wrote:
>
> My understanding is that 6015 does modify the accumulator -- from the
> manual
> (
>
> http://www.mirrorservice.org/sites/www.bitsavers.org/pdf/fabritek/402-1001-00_MP12refMan_1974.pdf
> )
> Function code 5(8) is interpreted as "...if th the addressed device is
> DONE, the next instruction in sequence is skipped, the contents of the
> device buffer are inclusive OR'd with the accumulator, and the result is
> retained in the accumulator..."
>
> So 6015 reads the next 8-bit quantity from the paper tape and ORs it onto
> AC.
>

Yes, it might very well. I wrote up a bit of code to test it out and don't
remember that being the case, but then again, it was late and I was
probably not thinking clearly.

Yeah, I was actually just looking at that again and the jump to 7755 is
> rather odd.  I think that's what stumped me a couple of years back and
> since I never got around to building the interface... I think I just
> assumed a couple of bits had gone south on my PROMs, to be honest.
>

Well, fear not for bad bits, unless three of these units have failing
PROMs. I think the ones in my colleague's unit are from the 1990s.
Impressive they were using these units up until then (or considerably
after, perhaps!).

That's interesting -- on my MP-12, the sync interface brings out (IIRC)
> three lines: clock, data in, and data out.  I'd be interested to know what
> hardware's hooked up to yours to provide all the goodies you have.
>

Indeed. All of the functions mentioned are all transferred via the
synchronous interface. I'm not sure how much decoding is done in the big
box versus the little box, but if I were a betting man, I'd say it's mostly
done in the big box. The little box has the seven 7-segment displays, a
paper tape reader, some arbitrary outputs, and some buttons. There are
three removable cards to make it all happen, and the DA-15 connector
supplies 120VAC as well as the synchronous data/clock lines to the little
box. There's an effort to reverse engineer the little box, then move up to
the big box. My colleague has already reverse engineered the 7-segment
driver board. It's my goal to get all of this information collected
together somewhere where it can be made available to all.

I think the size and surprising capability of the Fabritek makes it the
most clone-able of the TTL PDP-8s; much of the functionality of a
Straight-8 for instance, without the bulk. If we went with surface-mount
7400-series, as well as battery-backed SRAM, there's a good chance we could
improve upon the functionality (especially front panel operations!) and add
more memory, switchable ROM space, etc. It'll be a pipe dream for now,
though.

Kyle