PDP 8/e memory boards

From: Chuck McManis <cmcmanis_at_mcmanis.com>
Date: Thu Jul 27 18:23:52 2000

At 05:14 PM 7/27/00 -0500, Lawrence LeMay wrote:
>I'm trying to get my 8/E working. I've installed a basic set of boards:
>
>M8330
>M8310
>M8300 (with jumpers to the previous board)
>M837 memory extension
>M849 RFI shield

Not going to put an 8650 in yet? It can be useful if you have no lights
since you can fairly easily send characters out to it.

><memory>
>
>M8320 bus loads

Other than that it looks good.

>Well, first off, the extended address load switch seems to be broken, so
>I cant access extended memory (maybe I should yank the M837 board for
>now).

Ok before you declare it broken, consider what it does. When 'extd addr
load' is pressed the contents of switch register 6-11 are used to deposit
three bits into the data and address portions of the M837. Only the address
change bits show up in the upper three EMA lights on the address display.

> I tried a few core memory sets, but I dont think they are working
>properly, or possibly they arent configured properly. The memory sense/inhibit
>boards have jumpers for selecting the memory field, I'm guessing you have
>to start at field 0 and increment in continuous fields? What about 8K
>boards, do you have an 8K at field 0, and an 8k at field 2, and the boards
>would be covering fields 0 - 3? Is EMA 0 the high or low bit on the field
>selector jumpers (on the memory sense/inhibit boards)?

There are 8 "pages", 0 through 7. There is no requirement for them to be
contiguous. Every PDP-8 memory card I've seen (but I've not seen very many
third party boards) the EMA "jumpers" define the first page and if the
board is > 4K then they "cover" adjacent pages so when the 8K core stack is
set to page 0 it covers page 0 and 1, when it is set to 1 it covers 1 and
2, etc. Its conventional to have a page at 0 but I've got an 8 where the
first 4K was not working so it only has memory at page 1 and it seems to
work (when both the address and data EMA bits are set to 001!)

>Whats kinda confusing me is that I have a pair of 8K core memory sets
>that came from one computer a LONG time ago, yet they are configured
>for fields 1 and 2, whereas I think they should be 0 and 2.

That is confusing. I've noticed that overlapping core boards on the 8
doesn't seem to kill it, it just seems to waste memory.

>I also have a 16K core set, does anyone have any information on that
>board? The highgate docs appear to be for a hex wide 16k board.

Is it the hex wide that goes in the PDP-8a ? If so I believe I have
information on it in the PDP-8a handbook.

>I think the majority of lights on this computer are burned out, leaving about
>8 bulbs working. Is there any way to verify that using front panel controls
>and no memory?

Sure, put the switch register to all ones, press and hold "load addr", now
press and hold "load extd addr" all of the lights should be on. (except run
of course).

--Chuck
Received on Thu Jul 27 2000 - 18:23:52 BST