Tough to Diagnose issue with PDP 11/40 CPU
fritzm at fritzm.org
Wed Jun 29 19:39:01 CDT 2016
Do you have a KM11 maintenance card? Guy Sotomayor here sells kits
and/or assembled boards at
http://www.shiresoft.com/products/km11/KM11%20Replica.html. I built one
up myself based on a layout by Tom Uban at
The easiest way to get to the bottom of this since you have a nice,
short, repro case would be to step through the microcode with a KM11 and
see where it goes awry. From that point, its fairly easy to come of up
a list of boards to swap and/or chips to check.
If you want to go to the chip checking stage, you'll need some board
extenders and a logic probe, they are pretty cheap. Or you can grab a
surplus logic analyzer and some DIP clips off eBay if you want to get posh!
I just went through this process with my 11/45, it was pretty educational.
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