Tough to Diagnose issue with PDP 11/40 CPU

Noel Chiappa jnc at
Thu Jun 30 08:58:13 CDT 2016

    > From: William Degnan

    > The IOT step is bombing (?) and loops through the addresses:

This may be a pointless question, but just to clear the ground first: the CPU
is otherwise functioning reasonably well? E.g. it's not dropping the 020 bit
when reading words from memory? (That would convert the '220' new PC in the
vector to '200', and produce exactly the behaviour you are seeing.)

If it is otherwise more or less working, so this is specific to IOT trap
handling, I agree with Fritz - a KM11 would be a big help.


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