PDP-11/10 repair started

Noel Chiappa jnc at mercury.lcs.mit.edu
Tue Oct 6 11:54:03 CDT 2015

    > From: Tony Duell

    > Converting between genuine 20mA loop and RS232 is not that hard.

Yes, but I'm i) lazy, and ii) overwhelmed with other projects! :-)

    >> there's a 'SACK Timeout Module' (M8264) which I think performs the
    >> same function, but at the _start_ of the bus. (I say 'think' because
    >> this module is poorly documented - e.g. I don't know of anything which
    >> definitely states which slot to plug it into.)

    > I remember a 4 bit counter and LEDs, possibly to count errant grants

Yeah, that LED counter looks like a nice feature; I should find one, play
with it.

    > I always assumed it went in the last SPC slot

Well, looking at the print (it's in the 11/34 Vol. 2 set that's online), it
looks like it should work plugged in anywhere; the circuit just seems to look
for any BGn/NPG that's been on 'too long', and when it sees one, asserts

More complicated than the M9302 circuit, which depends on being last, plus
they could cram that onto the terminator, is probably why they switched to
the M9302 approach.


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