DEC PDP-12 Restoration Blog starting 1/1/19

08/24/19

Something strange is going on.

Sometimes OS/8 hangs, looping with a 6041 instruction waiting for characters to be sent out the serial console.

None of the usual programs like SPCWAR, TANK, and HANGMAN will run, the all loop with the 6041 instruction.

A toggle-in test for console output that uses the 6041 instruction works OK.

We swapped the M707 Teletype Transmitter module, but there was no change in the behavior.

Instruction test 1 works OK, including ringing the bell on the serial console.

Instruction test 2 works for a little bit, and then hangs in a loop at 0001 executing a JMP 0001.

Executing an interrupt when it should not?

Not executing an interrupt correctly?

Next week we will start at the beginning with all of the simple diagnostic programs to make sure that the processor is working OK.