29 Nov
2016
29 Nov
'16
5:56 p.m.
From: Peter Coghlan
Interrupts would be great to have
If you decide you need interrupts, the DLV11 (MP-00055) has a simpile
interrupt circuit built out of flops and gates.
However, I am puzzled by the BPOK and BINIT signals
being connected to
U7 even though they do not seem to get used ... I wonder is this just
because two tranceivers were left over and they might as well have
something connected to them that might come in handy later or is it
because I am failing to understand something properly?
Neither, but your first one is close! :-)
Actually, that design started as a CAD file (for KiCAD) that I got from Dave
B; I munged on it until it was what I wanted. Those two signals were
connected to that transceiver in Dave's original circuit; my design doesn't
(as you discovered) actually use BPOK or BINIT, so they just stayed connected
up, but unused.
there are rather more than 50 QBUS signals listed on
the top right of
the circuit diagram.
As Glen indicated, it actually takes 2 50-pin connectors.
I suppose the power rails and those labeled
"spare" are likely
candidates for omission.
I don't think they'd have carried power through that connector. The spare lines
might well be connected through.
I haven't checked the pinout of the 50-pin Berg headers (which were the
original, the 'D' connectors came later), but if they followed UNIBUS
precedent, every other wire in the flat cable will be a ground, to help
minimize cross-talk between lines with signals on them.
I was hoping that there would be lots of signal pairs
like SCSI
Well, the QBUS wasn't designed to go through a cable, originally it was
backplane only; so it doesn't have differential pairs, or anything like that.
Noel