Garnet-MM

Garnet-MM is a PC/104 digital I/O board with either 24 or 48 lines of I/O. It contains one or two 82C55 Ics, each having 3 8-bit I/O ports. Each 82C55 has its own 50-pin I/O header for external connections. Direction on all ports is selected by programming control registers built in to the 82C55 chips. All I/O lines are buffered with transceivers, whose directions are controlled by logic which responds to the direction control values written to the 82C55s. Each line is capable of sinking 64mA in a logic low state or sourcing 15mA in a logic high state. The board requires only +5V for operation.

Garnet-MM's I/O headers are organized to allow direct interfacing to OPTO-22's isolated I/O racks, including the G4 series, the PB16-H, -J, -K, -L, PB8H, and the PB24HQ. These racks and I/O modules allow up to 3000 VRMS isolation between the computer and the user's signals. All control signals, power, and ground on the Garnet-MM I/O header match the corresponding signals on these I/O racks, so a single 50-pin ribbon cable, such as Diamond Systems' C50-18, is all that is needed to make the connection.

The board provides access to interrupt levels 2-7 on the PC bus for real-time background applications. Interrupts can be generated in two ways. In Mode 0 operation, a rising edge on one of four interrupt lines causes the board to generate an interrupt request on the bus. In Mode 1 operation, the 82C55 generates interrupts in response to handshake signals between Garnet-MM and external circuitry.