Diamond Systems EMM-8PLUS-XT PC/104-Plus 8-Port RS232/422/485 Serial I/O Module

When a rugged stack has to talk to many serial devices at high data rates, eight ports on one module save both space and wiring effort. The EMM-8PLUS-XT is an eight-port PC/104-Plus serial module from the Diamond Systems Emerald-MM family, with rates up to 1.8432 Mbps and each port selectable for RS-232, RS-422, RS-485 or TTL level operation.

The module is built around an Exar XR17D158 octal UART on the PCI bus, with eight sets of 16C550-compatible registers and 64-byte transmit and receive FIFOs per port, so standard PC serial drivers apply. Plug and play handles configuration, a base address can also be set in software, and a single 32-bit read returns the interrupt status of all eight ports. The PCI slot is set by jumper, and as on all Diamond Systems boards the jumpers are paralleled with locations for 0 ohm resistors for shock and vibration resistance.

Each port on the EMM-8PLUS-XT has its own jumper block for protocol selection, with local-echo and non-echo RS-485 modes and jumper-selectable termination for RS-422/485. Rates reach 921.6 kbps in RS-232 mode and 1.8432 Mbps in RS-422 or RS-485 mode. Two 40-pin headers carry four serial ports and four digital I/O lines each, and the board adds a 16-bit programmable counter/timer. The EMM-8PL-XT is the eight-port PC/104 version for ISA stacks, and the MRC-424-XT adds Ethernet to PC/104-Plus.

Power is 5 V DC only, at around 160 mA typical with outputs unloaded, so no 12 V supply is needed for serial operation. The EMM-8PLUS-XT operates from -40 to 85 °C as standard, and Diamond’s C-DB9M-4 cable, two per board, breaks each header out to four DB9 male connectors.