Some CP converters have options for RS485 Half-Duplex and RS485 Full Duplex as well as RS422. What is the difference between RS485 Half-Duplex and RS485 Full-Duplex?
- RS485 Half-Duplex (2-wire) is the more familiar form of RS485 where two data lines (Data+ and Data-) are used to transfer data. The Connective Peripherals converter only drives the lines when it is transmitting data and so multiple devices can share the bus. Data can only flow in one direction at any time as there is only one pair of data lines.
- RS422 uses four pairs (TxD+/TxD-, RxD+/RxD-, RTS+/RTS-/CTS+/CTS-) allowing full duplex operation with data being sent and received and transmitted simultaneously, as well as handshake lines for flow control. The transmitter is always enabled to drive the TxD+/TxD- lines and so in RS422 mode the converter is used for a point to point connection. Note that the RTS/CTS lines may not be accessible on all models due to the available pins/terminals on the connector.
- RS485 Full-Duplex (4-wire) shares some features with RS485 Half-Duplex and with RS422. Like RS422, it allows full-duplex operation via TxD+/TxD- and RxD+/RxD- pairs but does not have RTS/CTS lines. Like RS485 Half-Duplex, it only enables the transitter when sending and so multiple devices can share the same bus, each only driving the TxD+/TxD- pair when sending data and otherwise listening only.