1 Oct
2014
1 Oct
'14
7 a.m.
From: David Riley
Looking at the PMI pins in the KDJ11-B manual, it
looks like there are
signal lines on the D2 pins for the memory. That's a +12v pin for Qbus.
What I just cannot fathom is why they used D2! PMI is only like 14 signals or
so (plus normal QBUS signals like BDALxx), and there are heck of a lot more
than 14 available pins on the CD that _do not_ conflict with the normal QBUS
power, etc. (You lose xS1 and xB2, but the rest all look OK, although if you
want to stay away from +5 you lose a few more.)
Someone must have a bad case of brain fade, is all I can think.... But I'm
still pretty incredulous that nobody else caught it before it was too late.
Maybe it was deliberate - they hoped to increase sales through people burning
boards out, plugging them into the wrong backplanes? (Tongue 3/4 in
cheek... :-)
Noel
1 Oct
1 Oct
8:54 a.m.
On Oct 1, 2014, at 10:00 AM, Noel Chiappa <jnc at mercury.lcs.mit.edu> wrote:
What I just cannot fathom is why they used D2! PMI is
only like 14 signals or
so (plus normal QBUS signals like BDALxx), and there are heck of a lot more
than 14 available pins on the CD that _do not_ conflict with the normal QBUS
power, etc. (You lose xS1 and xB2, but the rest all look OK, although if you
want to stay away from +5 you lose a few more.)
I had exactly the same thoughts. +5v is also the same pin as it is on
Unibus; Qbus shares Unibus' defined +5v and GND pins and adds a few more
dedicated grounds (MUB is a different matter, of course). I'm honestly
a little surprised they didn't make the power pins a little more broadly
compatible (or at least less likely to cause damage) in general, but
presumably it was a matter of many different engineering teams working
on different standards over many years.
Someone must have a bad case of brain fade, is all I
can think.... But I'm
still pretty incredulous that nobody else caught it before it was too late.
Maybe it was deliberate - they hoped to increase sales through people burning
boards out, plugging them into the wrong backplanes? (Tongue 3/4 in
cheek... :-)
I had that thought as well.
- Dave
1:30 p.m.
I had exactly the same thoughts. +5v is also the same
pin as it is on
Unibus; Qbus shares Unibus' defined +5v and GND pins and adds a few more
dedicated grounds (MUB is a different matter, of course). I'm honestly
a little surprised they didn't make the power pins a little more broadly
compatible (or at least less likely to cause damage) in general, but
presumably it was a matter of many different engineering teams working
on different standards over many years.
Reminded me, alas, of the time when I was younger and evn mroe foolish
and repairing an RK11-C. I had pulled one fo the namy flip-chip cards to
inventigate it, and decided to power ir up by stickign it in a slot in an
otherwise empty Unibus backplane that was conencted ot the PSU. +5V and
Groudn were in the right places, I'd checked that.
WHat I had not spotted was that there's -15V on pin B2 of said
connectors. And this was a logic input on the card I was testing (I think
it was the carry inptu to a 7482 adder, it was certainly _an_ input to a
7482).
RIP 7482, not an easy chip to find.
-tony
3736
days inactive
3736
days old
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