To aid in the repair of the DEC PDP-8/L and PDP-8/I systems Warren Stearns made a device for testing most the FlipChip boards used in these systems.
The core of the tester is the five Microchip MCP23S17 16-bit input/output port expander with interrupt output chips. Each of these chips has a different address on the SPI bus so they are individually addressable.
Standard 0.1" jumpers connect the pins on the FlipChip socket to the SPI chips so that individual signals can be disconnected for debugging.
Additional resistors are located on the board that can be connected to high-current signals to provide an additional load.
Warren wrote a SPI driver that Bit-Bashes the SPI signals on a standard PC parallel port. Warren also wrote and application that reads a line of I/O codes from a test vector file, configures the I/O pins on the SPI chips, writes the output pins, and compares the input signals to the expected states in the line codes from a test vector file. If it compared OK it reads the next test vector and tries it again.
Some of the simple FlipChips have just a few test vectors. Complicated FlipChips, like the M220, have over 2,000 test vectors.
Future development work could include converting the positive logic signals to negative logic so B/R/S versions of FlipChips could be tested. Many of the FlipChips, mostly the A and G versions, have analog circuitry so analog I/O would be useful.
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