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RS-Slide19

The RS-485 full duplex multi-point network uses an additional twisted pair so that the master can transmit and receive on separate busses. This network uses an RS-422 multi-drop configuration - with a single termination resistor - for the master to poll the slaves, and a multi-point RS-485 configuration for the slaves to respond to the master. Throughput is higher than on the half duplex network, because the previous slave is responding to the master on the lower bus while the master polls the next slave on the top bus. The master transceiver is a full duplex, RS-422 type without enable pins. Slaves must be RS-485 full duplex types with driver enable pins, because they all share a transmit bus. Slave receivers are typically left always enabled, because there is no “echo” to suppress as a slave’s receiver does not connect to the same bus as its transmitter.

PTM Published on: 2016-01-04