2 Nov
2018
2 Nov
'18
10:43 a.m.
On Fri, 2 Nov 2018, Columbia Valley Maker Space via cctalk wrote:
Hello everyone - my first post, so be easy on me!
I have just acquired a PDP8/a and a Remex punch tape reader. The unit
starts up and displays some data on the displays, and that is about all
I can tell you.
I am going to do some googling about this, but I am looking for basic
initial tests .... something I can enter via the keypad.
I learnt some basic programming in 1978 on a PDP8, but that was the last
time I touched one, so if you are going to suggest some tests, I need
complete instructions. I don't know how to modify a memory location, let
alone enter and check a program. I will pick all this back up very
quickly and I do use computers in my work a lot - I am also an
electronic hobby guy and have been for years. My point is I am OK with
component level measurements, I have a scope and probes, etc.
So there you go - hope to hear back form you guys.
So: power on. Power key up, boot & panel-lock down.
Display memory:
MD DISP
You should see the MD LED light up.
Enter an address:
0200
then LA then E-THIS
That will give you the value of location 0200.
Enter a number - e.g. 1234 then D-Next will enter that number into the
displayed address and advance the program counter by one.
Simple program:
2 0100 *100
3 00100 0000 COUNTER, 0
4
5 0200 *0200
6 00200 7300 CLA CLL
7 00201 3100 dca COUNTER
8
9 DELAY,
10 00202 2100 ISZ COUNTER
11 00203 5202 JMP DELAY
12
13 00204 7001 iac
14 00205 5202 JMP DELAY
Numbers in the 3rd column are the ones you enter in.
So MD DISP, then:
0000 LXA
0200 LA
7300 D-Next
3100 D-Next
2100 D-Next
5202 D-Next
7001 D-Next
5202 D-Next
Check with
0200 LA
D-This (Should see 7300), then D-Next, etc.
Start:
0000 LXA
0200 LA
INIT
RUN
then display the accumulator (AC DISP)
and you should see it counting in octal
It was probably controlling a CNC machine until recently - that
combination was very popular and what mine was used for until it
was decomissioned only a few years back. There are still some
in-use today!
Mine:
https://lion.drogon.net/IMG_20180128_095121.jpg
I don't have the tape drive, and I did a one-wire mod to the IO board to
allow for TTL level serial out so I could connect it to a TTL serial USB
adapter on a Pi.
Always check the display mode - make sure in MD mode when changing or
looking at memory.
Have fun, and good luck!
Gordon
