21 Oct
2021
21 Oct
'21
11:56 a.m.
A couple of comments on a number of things touched on in this thread:
From: Nigel Johnson Ham
Ah, well there you see the end of my technical
knowledge.
My observation is that since varying QBUS PDP-11 CPU's can be swapped in and
out (unlike UNIBUS PDP-11's, where the CPU's backplane and front panel are
not interchangeable between models), and QBUS machines were therefore often
upgraded over their lifetime by switching in a CPU, when starting out with a
new machine, one should _always_ start by working out what kind of QBUS
backplane one has, and going from there.
The BA23 is the one that's part Q/CD and part Q/Q.
No, I don't know if the CPU is good (it is a
dual-width KDF11-A btw),
...
I do have an 11/73 dual width board arriving tomorrow
...
it is crashing into ODT and not accepting input from the console, which
I remember was a symptom of no bank 0 memory.
That's true of all LSI-11's (and it threw me for a while when we first ran
across it), but KDF11-A's and KDJ11-A's work fine with _no_ working memory in
the machine: i.e. just a CPU board and a console will work fine (as in, ODT
works, and one can examine what few registers are on the bus).
(I had previously fried the KDF11-A; just tried the KDJ11-A. Probably the
KDF11-B and KDJ11-B work too, but I'm toolazy to try them at the moment.)
So if a machine with _just_ a CPU and console doesn't work, you've got a
problem; but it shouldn't be too hard to find it, with only two boards.
From: Joshua Rice
> "many boards designed for Q/CD slots (such as
PMI cards) do not avoid
> the QBUS pins on the CD connectors which contain 'hazardous' (to TTL
> circuitry) voltages."
I should note that that text is somewhat questionable; I recently checked the
list of PMI pins, and I didn't see any that conflicted with 12V pins on Q/Q
slots. But definitely plugging a PMI card into a Q/Q slot will damage it:
MicroNote 28 says "MSV11-J MODULES CAN[NOT] BE PLACED IN A Q/Q BACKPLANE
SLOT. IF THIS IS ATTEMPTED PERMANENT DAMAGE WILL BE DONE TO THE BOARDS".
From: Jerry Weiss
I don't believe ODT is dependent on working
memory.
On LSI-11's, it us. Location 0 must respond to a read cycle, or the
CPU will spin trying to read it, _before_ ODT will start.
Noel