[vcf-midatlantic] PDP 11/40 finally got it working better-er
billdegnan at gmail.com
Wed Jun 29 23:51:15 EDT 2016
For many years I have been working off and on to get my pdp 11/40 running.
I was having trouble getting past "chase the lights" and simple tests. I
was even able to load in a papertape. It was in memory ok but never ran
.I got a lot of good advice but nothing seemed to work. I made sure
everything was correct on the backplane and RAM was ok. Some important
diagnostics simply would not run however. I was stuck.
After a lot of spinning my wheels finally I discovered the CPU was wired
for a KJ11 module (stack limit register) but I did not have one installed.
I was having problems with code that included the stack so there you go
makes sense now....but it took a while. Part of the problem is that I
always thought the KJ11 and KW11-L (line time clock) were always paired
up. This was not a logical reasoning, it was only because I always saw
them paired that way and I assumed they were a set. I even had in the past
tested the system with both installed but it froze things so I abandoned,
never thought to try just one or the other alone. But apparently that
would have been the ticket, my system CPU was wired for the KJ11 only. I
tried just the M7237 and poing it worked. I finally was able to run
complex diagnostics and I even downloaded BASIC from papertape and ran it
(much faster than 11/05 btw)
Here is the page with more info
Next I can try to boot an RT11 RL02 pack from an RL11 controller (M7762).
If anyone is going through the same thing how to troubleshoot a lot of the
UNIBUS stuff let me know happy to try to help.
Twitter: @billdeg <https://twitter.com/billdeg>
Youtube: @billdeg <https://www.youtube.com/user/billdeg>
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