EIA-422 (formerly RS-422) is a serial data communication protocol which specifies 4 wire, full-duplex, differential line, multi-drop communications. It provides for balanced data transmission with unidirectional/non-reversible, terminated or non-terminated transmission lines. In contrast to RS485 (which is multi-point instead of multi-drop) EIA-422 does not allow multiple drivers but only multiple receivers.
Several key advantages offered by this standard include the differential receiver defined in RS-423, a differential driver and data rates as high as 10 Megabaud at 12 metres (40 ft).
The mechanical connections for this interface are specified by EIA-530 (DB-25 connector) or EIA-449 (DB-37 connector), however devices exist which have 4 screw-posts to implement the transmit and receive pair only. The maximum cable length is 1200 m. Maximum data rates are 10 Mbit/s at 1.2 m or 100 kbit/s at 1200 m. EIA-422 cannot implement a truly multi-point communications network (such as with EIA-485), although only one driver can be connected to up to ten receivers.
A common use of EIA-422 is for RS-232 extenders.