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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 10M baud at 40 feet.
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 1200m. Maximum data rates are 10Mbps at 1.2m or 100Kbps at 1200m. 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.
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