Answer: The IP521 is designed to operate as a full duplex RS422 or RS485 device. Full duplex RS422 device require a Four wire connection; Transmit + and - and Receive + and -. In full duplex design a device can be transmitting and receiving information at the same time. To operate properly in half duplex mode the UART must be designed to receive either special handshaking wires or character commands to know if it is acceptable to transmit or be prepared to receive data. The IP521, although not designed for it, can be connected as a half duplex design by connecting RX and TX lines together. To do this, the application software is required to handle the decision to switch the device into either transmit or receive mode.