The IMP8980D can switch data from channels on ST-BUS inputs to channels on ST-BUS outputs and simultaneously allows its controlling microprocessor to read channels on ST-BUS inputs or write to channels on ST-BUS outputs (Message Mode). To the microprocessor, the IMP8980D looks like a memory peripheral. The microprocessor can write to the IMP8980D to establish switched connections between input ST-BUS channels and output ST-BUS channels or to transmit messages on output ST-BUS channels. By reading from the IMP8980D, the microprocessor can receive messages from ST-BUS input channels or check which