PDP-11/10 repair started

tony duell ard at p850ug1.demon.co.uk
Tue Oct 6 12:04:45 CDT 2015

>     > Converting between genuine 20mA loop and RS232 is not that hard.
> Yes, but I'm i) lazy, and ii) overwhelmed with other projects! :-)

True, but sometimes (and I have been guilty of this) it takes longer to post and moan
about the problem than to dig into the junk box, grab the soldering iron, and fix it.

[SACK timeout board]
> 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

I can't be bothered to download the prints for just that one board (see above ;-))

But if it behaves as you describe, it would appear that if placed at the remote
end of the bus it could lock the bus by forcing SACK/ asserted (as the M9302 does)
if a grant chain is open, whereas if it is placed at the CPU end it can't. 


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