18 Jun
2005
18 Jun
'05
10:54 a.m.
On Sat, 18 Jun 2005 "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 KK8A cpu takes a single slot, while you need a total of four for the
KK8E, which obviously is an advantage, especially in a small 8/a system,
where you only have 12 slots.
The KK8E have a 1.2uS cycle time, while the KK8A have 1.5uS. Also, the
KK8E can be extended with the EAE option, while the KK8A cannot.
The KK8A is also microprogrammed. Might be harder to repair (depending on
what is broken) but it might also be a bit more reliable. It probably
draws a bit less as well.
You can replace one with the other. Instruction wise, they are totally
compatible. There are some undocumented stuff that they behave differently
on, so you can from software tell which CPU you have, but in normal life,
it don't make a difference.
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.
The boot roms hold very little data, and they simulate the front panel
signals for loading into memory. I think you have a total of 64 words, or
something like that.
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.
Not sure what you're talking about here. The power regulators for the 8/a
have a card-like connector, which you have the mate for on the rear side
of the backplane. I suppose you're talking about those. Otherwise I have
no idea. The power regulators are neccesary, otherwise nothing works.
The core memory for the 8/a also require some voltages on the fifth slot
in the backplane, which don't exist on an 8/e.
Johnny
Johnny Billquist || "I'm on a bus
|| on a psychedelic trip
email: bqt at update.uu.se || Reading murder books
pdp is alive! || tryin' to stay hip" - B. Idol