23 May
2003
23 May
'03
5:07 a.m.
--- Brian Chase <vaxzilla(a)jarai.org> wrote:
I'd really like to design and build a PDP-8 clone,
since the real
ones command such hefty prices on eBay. I've mostly given up on
getting my own 8/F or 8/M.
If you are after the experience of having a PDP-8 clone, not the
experience of designing your own from scratch, there's the SBC-6120
at http://www.sparetimegizmos.com/ I don't know if there are any
boards left (we had a group buy some time ago; pictures of mine are
at http://penguincentral.com/retrocomputing/pix/sbc6120/ ), but it's
a nice little machine that is easy to get up and running. I'll be
demoing mine at a computer history exhibit at a science fiction
convention this weekend (alongside a PDP-8/L w/ASR-33 and PC04).
The CPU is an Intersil/Harris 6120 - commonly described as a PDP-8/e
on a chip. They are still available, new, for about $50. There's
also the 6100, available much cheaper (several listmembers purchased
them by the *tube* recently), but the 6100 lacks on-board EMA support,
among other things (it used a 6102 in the VT-78 for that).
If there are no more SBC-6120 blank boards available, it's possible to
order your own (expensive for small runs) or use the schematics as a
starting point and build your own with wire-wrap or point-to-point.
Everything on the SBC-6120 is available from modern stocks, although the
64Kx4 SRAMs (6408?) are somewhat hard to find now - rolling your own
design means being able to use just about any SRAM you can find. It
does require three GALs, though there are people on the list who can
provide them for a nominal cost (2 x 16V8 + 1x 22V10). It's a fully
CMOS design - mine draws 175mA, and I have run it off of batteries.
The only thing it "lacks" at the moment, compared to a PDP-8/e is
non-volatile main memory (but some -8s had MOS anyway, not core), and
blinkenlights.
Alternately, there are a few projects out there you could borrow from
to implement a PDP-8 core in an FPGA. Because of the simplicity
and the extensive documentation, it was frequently assigned as a
student project.
Good luck,
-ethan
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