18 Jun
2005
18 Jun
'05
9:44 a.m.
On 6/18/05, Joe R. <rigdonj at cfl.rr.com> wrote:
Anyway I've been reading the PDP-8a User's
Manual and trying to figure
out what all I have here and I have a question about the PDP-8 CPUs. DEC
offered two different CPUs for the PDP-8, one is the KK8-A which is a
single M8315 card. The other is the KK8-E which consist of an M8300 and
M8310 cards which are the CPU and an M8320 Bus Loads card and a M8330
Timing Generator card. Can someone explain the differences between the two
and why DEC offered two very different CPUs for the 8? Can I replace
simply the M8300/8310/8320/8330 cards with the M8315?
The biggest differences between the KK8A and KK8E are...
o KK8E can take an EAE, the KK8A cannot
o KK8E is 1.2 uS per cycle, KK8A is 1.5 uS
o KK8A takes one hex slot, KK8E takes 4 quad slots.
There may be an OPR instruction difference here and there, but unless
you have some weird software that really depends on what CPU it's
running on, that won't make a huge difference. I have no idea about
relative cost, new, but I'm sure back in the day, there was a price
differential which may have affected a purchase or two.
So unless you have a burning reason to go with a KK8A, I would think
that if you already have a KK8E, you might want to stick with it.
I also have a question about the diagnostic paper
tapes. Does anyone have
a ROM emulator or other way to load the diagnostics without using a PT
reader? Yes, I know there are some SIMPLE diagnostics that can be loaded
from the Programmer's Panal but I concerned about the more extensive
diagnostics. In fact, I'm wondering if anyone has tried burning the
diagnostics into PROMs and installing them in place of the Boot Roms on the
M8317 card.
I think the boot proms are too tiny to hold any meaningful diagnostics
- 32 words per switch position? (4 boot devices per ROM set, IIRC)
By the time you are getting into instruction set tests, etc, you are
at the few-hundred-word size. By the time the M8317 had come out, DEC
had shifted their emphasis from running extensive paper-tape tests in
the field to booting XXDP (PDP-11) and whatever the floppy-based PDP-8
diag suite was called If it couldn't boot the floppy, there were only
a couple of boards to swap, so they opened up their field-service
suitcase, replaced as much of the processor as required, got the
customer running again, then sent the boards off to the depot for
diagnosis and repair offline.
There's no reason you _couldn't_ build a PROM emulator, but at that
stage you might as well turn a modern machine into a paper tape
emulator and do it that way.
Can anyone explain the purpose of the small card
that plugs into the back
of the chassis near the power regulators? It's not mentioned in the User's
Manual and I don't even know it's name. Thom says that it controls the
power and the machine will be completely dead if it fails but that's all
that I know about it.
Hmm... I don't recognize it from your description... could you post a
picture of it?
-ethan