The GE Fanuc / Radstone PME SIO-4 Serial Communications Controller features sixteen independently programmable input/output channels provided by eight type 68681 Dual Universal Asynchronous Receiver/Transmitters (DUARTs). Each channel has a control structure associated with it in the local memory. A host controls the SIO-4 by accessing control words within these structures in the local memory. The sixteen RS-232C channels leave the front panel of the SIO-4 via two 64-way connectors.
The SIO-4 appears to the host processor as 1 Mbyte of RAM mapped into the VMEbus memory map on a 1 Mbyte boundary. On-board Dual-In-Line (DIL) switches select the address used. The card has full VME interrupt generation and handling capabilities, and a location monitor facility. As a slave, the card can be set by jumpers to respond simultaneously in the A24 and A32 address spaces.