On Sep 30, 2014, at 20:05, jnc at
mercury.lcs.mit.edu (Noel Chiappa) wrote:
Off-topic somewhat, but I wonder why DEC put PMI
signals, etc on power pins
(I assume that's what zaps a PMI/etc card plugged into a Q/Q slot). Surely
there are enough pins which are bus lines, etc, which one could use? Yes, the
machine probably wouldn't work if one plugged such a card into a Q/Q slot,
but you wouldn't zap boards...
Indeed, that's actually something I'm planning on figuring
out; my current quandary is mapping Unibus pins against
Qbus pins in order to figure out why one might cook the
other (main answer I see so far: Qbus has a standard +12v
power pin on what is normally a data pin for Unibus, but
it's nothing that can't be worked around with modern
electronics). Next step will be figuring out what's going on
with common CD bus pins that cause the same problem; it
may actually be the same thing, but I haven't looked closely
enough at a full pinout of the CD bus to get an idea yet.
> CB2 is
tied to DB2, and the two feed (through a jumper which is
> normally removed) special power (-5V) for a particular kind of EPROM
-5v is an optional rail on Qbus, anyway.
Actually, I think AB2/BB2 are 'normally' -12V - although not all power
supplies provide the -12 - e.g. the BA11-N only does +5V and +12V.
Maybe that's what it was thinking of, along with +5v-battery.
My H9270 certainly gets along running off of a PC
power supply's drive cables just fine.
In general, as
long as there are removable grant jumpers for the CD
lanes
But not all quad cards have removable grant jumpers - e.g. the BDV11 doesn't.
(Not sure why it even _has_ grant jumpers, given that one would usually make
it the last card, especially since it has pull-ups - but I guess it's in case
one doesn't.)
You can install it without the terminators so that, for
example, you could plug it into the first of several boxes
on an extended bus; the control switches are pretty
handy in that situation. But it's also a fairly early Qbus
card.
- Dave