PDP-12 Restoration at the RICM

From: Mike Ross: Tuesday, May 26, 2015 5:48 AM Warren's tester is similar in basic capability to the one that Henk and I did some time ago, with some additional circuitry that's useful for "load testing" -- telling the difference between an M6xx and an M1xx card, etc. Basically, ours had some I/O registers that you could set to control I/O direction, and some latching transceivers to drive test vectors to the module and read back results from the module. This was done on a platform driven through a serial port talking to a 6802 microprocessor. Warren's design, as mentioned by Michael, uses a set of SPI ports, talking to 23S17 chips, which allow you to configure I/O direction, set the test vector, and receive the result. In addition, he's set up some LEDs and various loads and pull-ups, which can be configured as needed to more accurately load the module. This all works quite well for "slow" testing of combinatorial logic. It's more cumbersome to come up with test vectors for sequential logic, though it can (usually) be done. Level converters can be added for B/R/S series modules, though the design of those while preserving the ability to set the I/O direction is a bit of a pain (in terms of both cost and component count). I think for more general testing (Gxxx?), it may be necessary to have proper "pin drivers", somewhat like those used in PROM programmers. For more dynamic testing, some me kind of local processing is probably needed to judge the dynamic properties of a response, and it may not be good enough to have to serialize and un-serialize the data. A shortage of gumption and relevant skills has kept me from being helpful for a while now... Mine are all 12 bit, but me too. Vince