The RICM has a PDP-8/I that was originally used to test vacuum at the United Electronics Company in Newark, N. J.
http://www.ricomputermuseum.org/Home/equipment/pdp-8-i
At the end of its working life it sat in an abandoned building for several years before it was rescued and donated to the RICM. Unfortunately the poor environmental conditions led to lots of corrosion. It was quite an effort to get it running, including repairing or replacing 58 flipchips. Once it was running again it has been very reliable.
We had not run the system for a few months, so two weeks ago we tried to boot DMS on it. It wiggled the DECtape, but failed to boot. It was stuck in a loop waiting for the TC01 to do a Data-Break. Further investigation showed that the problem was actually in the processor. The code reads Status Register A, executes a CIA to turn the status into a 2s compliment, TADs it to the expected value, and does a SZA to make sure that the register contents match the expected value. It didn't. We eventually found that the IOP 2 signal was missing at the TC01, so it would not read the status register. Wiggling flexprint cables and cleaning the gold fingers on the M651 bus drivers fixed that problem. This is an example of the corrosion problems with this system.
The MAINDEC DITCA TC01 BASIC EXERCISER first writes, reads, and compares the status registers before it starts testing the TC01. This part failed right away. We found that the CIA instruction didn't always work. Cleaning the gold fingers on the M617 in slot E32 fixed the CIA instruction. Corrosion again. We ran MAINDEC D01C Instruction Test 1 and MAINDEC D02A Instruction Test 2 for quite a while without errors. MAINDEC DITCA TC01 BASIC EXERCISER failed immediately with a register compare problem.
So, it looks like the CIA instruction works fine during the processor instructions, and fails in the TC01 BASIC EXERCISER. We made a little loop that loaded the switch register into the AC, and looped doing CIAs. This worked OK.
Maybe it is an issue when executing an IOT and then a CIA?
http://www.ricomputermuseum.org/Home/equipment/pdp-8-i
At the end of its working life it sat in an abandoned building for several years before it was rescued and donated to the RICM. Unfortunately the poor environmental conditions led to lots of corrosion. It was quite an effort to get it running, including repairing or replacing 58 flipchips. Once it was running again it has been very reliable.
We had not run the system for a few months, so two weeks ago we tried to boot DMS on it. It wiggled the DECtape, but failed to boot. It was stuck in a loop waiting for the TC01 to do a Data-Break. Further investigation showed that the problem was actually in the processor. The code reads Status Register A, executes a CIA to turn the status into a 2s compliment, TADs it to the expected value, and does a SZA to make sure that the register contents match the expected value. It didn't. We eventually found that the IOP 2 signal was missing at the TC01, so it would not read the status register. Wiggling flexprint cables and cleaning the gold fingers on the M651 bus drivers fixed that problem. This is an example of the corrosion problems with this system.
The MAINDEC DITCA TC01 BASIC EXERCISER first writes, reads, and compares the status registers before it starts testing the TC01. This part failed right away. We found that the CIA instruction didn't always work. Cleaning the gold fingers on the M617 in slot E32 fixed the CIA instruction. Corrosion again. We ran MAINDEC D01C Instruction Test 1 and MAINDEC D02A Instruction Test 2 for quite a while without errors. MAINDEC DITCA TC01 BASIC EXERCISER failed immediately with a register compare problem.
So, it looks like the CIA instruction works fine during the processor instructions, and fails in the TC01 BASIC EXERCISER. We made a little loop that loaded the switch register into the AC, and looped doing CIAs. This worked OK.
Maybe it is an issue when executing an IOT and then a CIA?