10 Jun
2003
10 Jun
'03
9:07 p.m.
Ethan,
there's a M720 circuit diagram on microfiche in my collection. I'll try
to take a picture of the fiche viewer's screen with my digital camera,
but it's a bit difficult due to illumination varying widely across the
screen. In addition, the newer rev level is printed blurry on the film.
I'll try again tonight, if I get out of the office in time.
As far as I can remember from looking at the fiche yesterday, there are
three SN7400N chips and one SN7460N in the circuit, together with four
transistors, a couple of diodes and passive parts. Doesn't look too
complicated.
Andreas
Ethan Dicks wrote:
Both of these are likely to be labelled "memory
detection". I have
seen both appear in module listings (and, from reports, in the real
world) in slot B10 of a PDP-8/i. I keep entertaining delusions that
I will be able to upgrade my -8/i to 8K someday. This module is the
only one that I cannot borrow from another machine or my pile of spare
parts.
ISTR the M702 contains a delay line and some buffering TTL. I'm told
that the M720 contains some TTL chips and a few transistors.
My goal is to understand them well enough to fabricate a substitute,
either from scratch, or by co-opting some blank spaces near slot B10 and
using DEC M-series modules.
Thanks,
-ethan
--
Andreas Freiherr
Vishay Semiconductor GmbH, Heilbronn, Germany
http://www.vishay.com