Space Shuttle Databus Interface for PC/ISA Computers

Description

The MDM (Multiplexer/ Demultiplexer) databus provides serial communications between a Space Shuttle Payload General Support Computer (PGSC) and various subsystems. The MDM interface consists of a serial databus and three discrete signal lines: Message In, Message Out and Word.

The PC-MDM-1 is an IBM PC/AT (ISA) interface card that is capable of transmitting and receiving up to 32 data words in accordance with the MDM databus protocol.

The PC-MDM-1 may be configured to be either a bus controller or a remote terminal. As a bus controller, the host computer and PC-MDM-1 simulate the PGSC by controlling message traffic over the MDM databus. As a remote terminal, the PC-MDM-1 simulates a subsystem and responds to the bus controller. In either mode errors are detected and flagged.

Provided with the PC-MDM-1 are Windows® 95/NT and MS-DOS® drivers and libraries of C language functions that access data and control the card. The host computer can poll for the status of messages or use interrupts. A companion card, the PC-SSB-1, is also available for the Space Shuttle MIA bus.

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