Diamond Systems OMM-DIO-XT 48-Channel Low-Cost Wide Extended Temperature Digital I/O PC/104 Module

Reading status contacts and switching indicators and relays is the most common digital I/O job, and it rarely needs counters or FPGA logic. The OMM-DIO-XT is the Onyx-MM-DIO from Diamond Systems, a low-cost PC/104 digital I/O module with 48 lines, and the plain-digital member of a range that also includes the FPGA-based GPIO-MM-XT series.

Two 82C55 chips each provide 24 lines as three 8-bit ports, A, B and C, giving 48 lines programmable for input or output. A control register on each chip sets the port directions and operating modes. Mode 0 gives basic input and output without handshaking, which suits status signals and switching; Mode 1 adds strobed I/O on Ports A and B with handshaking on Port C; Mode 2 makes Port A a bidirectional bus; and bit set/reset changes any Port C bit without reading and masking the port.

Every line has a 10K pull-up resistor, and on power-up or reset all ports return to input and are pulled high, so no line drives the field wiring until the software configures it. Outputs source or sink 2.5 mA per line. Two 50-pin headers carry 24 lines each, organised as three 8-bit ports with +5 V and ground pins, and each takes one C-50-18 ribbon cable. The OMM-XT adds three 16-bit counter/timers and programmable interrupts to the same 48 lines, and the GPIO-MM-21-XT raises the count to 96.

The OMM-DIO-XT runs on +5 V at 100 mA typical with outputs open and operates from -40 to 85 °C. It uses the 8-bit PC/104 bus, stacking on Diamond hosts such as the HELIOS SBCs, and Diamond quotes an MTBF of 1,714,901 hours. The free Universal Driver C library and example programs with source code cover all the digital I/O features.