The circuit shown on this slide is a half duplex, RS-485, multi-point network where all the transmit and receive devices reside on the same bus. Because of this, half duplex transceiver ICs with the driver outputs and receiver inputs internally connected are utilized. Additionally, driver enable functions are required to tri-state inactive transmitters. In the half duplex network shown, the master first uses the bus to poll a particular slave, and then it relinquishes the bus to the addressed slave for a response. This bidirectional use of the single bus limits throughput, but the advantages are a less expensive network that is much simpler to install. Enable and disable timing is critical, because the master cannot poll the next slave until the slave currently transferring data has relinquished the bus. The half duplex bus has two termination resistors – one at each end – because data can be transmitted in either direction, and as before, unterminated stub lengths must be kept electrically short. The receiver enable pin, RE#, is used for echo suppression. If a node does not want to echo back the transmitted data via its receiver, then RE is driven high during transmission. A transceiver with DE and RE# shorted together for a single pin direction control line guarantees echo suppression.