Diamond Systems OMM-XT 48-Channel Digital I/O and Counter/Timer PC/104 Module

Some control tasks need more than static on/off lines: latching data on an external strobe, raising an interrupt when it arrives and timing the events in between. The OMM-XT is the Onyx-MM digital I/O and counter/timer module from Diamond Systems, a PC/104 board that combines 48 digital lines, three counter/timers and three programmable bus interrupts. It sits alongside the FPGA-based GPIO-MM-XT series in Diamond’s digital I/O range.

Two 82C55 chips provide the 48 lines as six 8-bit ports, programmable for input or output in groups of four or eight, with 10K pull-up resistors on every line; all ports reset to input at power-up. Mode 0 handles basic I/O, Mode 1 adds strobed I/O with handshaking and interrupt signals on Ports A and B, Mode 2 turns Port A into a bidirectional bus, and bit set/reset changes single Port C bits without masking.

The three 16-bit counter/timers use an 82C54, with inputs switched in software between external signals, the 4 MHz on-board oscillator and other counter outputs, so counters can cascade to 32 or 48 bits. A second register routes up to three PC/104 interrupt lines from counter outputs, digital lines or an external input, which lets a counter interrupt the host at a programmed rate. Two 50-pin headers carry 24 digital lines each, and a 14-pin header carries the counter and interrupt signals. The OMM-DIO-XT keeps the 48 lines without counters, and the GPIO-MM-XT steps up to 64 lines and ten counters.

The OMM-XT runs on +5 V at 120 mA typical and operates from -40 to 85 °C. It uses the 8-bit PC/104 bus, so it stacks on Diamond hosts such as the ATHENA IV SBCs, and Diamond’s Universal Driver library for C supports digital, interrupt-driven and counter/timer operations with example programs.