RS-422

Definition of RS-422 in The Network Encyclopedia.

What is RS-422?

A high-speed full-duplex serial interface that uses balanced lines and has more immunity from noise than the RS-232 interface. (An unbalanced version called RS-423 is less frequently implemented.) RS-422 is used in industrial environments with a lot of electromagnetic interference (EMI) or where more than two serial devices need to be chained together. It is typically used for high-speed synchronous communication between data terminal equipment (DTE) and multiple daisy-chained data communications equipment (DCE).

RS-422 was originally designed to supersede RS-232, but they now coexist. RS-422 typically transmits data at rates of 230 Kbps, but the speed can be increased to around 1 Mbps. The maximum distance for an RS-422 connection is typically 300 meters. RS-422 cables typically have 25 wires and use DB37 or DB9 connectors.

NOTE

Related Electronic Industries Alliance (EIA) standards include the following:

  • RS-449:
    Specifies the pinning for RS-422 when DB37 connectors are used.

     

  • RS-485:
    Expands RS-422 to include balanced multipoint serial communication using tristate drivers.

     

  • RS-530:
    Specifies the pinning for RS-422 when DB25 connectors are used. Note that RS-530 cables look like RS-232 cables but are not compatible with them.

     

RS-422 and RS-423 are compatible with the International Telecommunication Union (ITU) V.11 and V.10 standards, respectively.