RS-422 is a point-to-point serial communications standard that defines a differential (or balanced) interface using two separate wires for each signal. Differential signals on twisted pair cables allow very high data rates in environments despite electrical noise and varying ground potentials. Signal levels are compatible with RS-485 so equipment is often configurable for either standard. The RS-422 standard does not define mechanical connections or assign pin numbers, but often DB-9 connectors are used. Typically, two wire pairs are used to accomplish two-way communications.
In some cases hardware handshake lines (RTS, CTS) are included in an RS-422 interface. Each signal requires one twisted pair.
RS-422 Tech Tip: Always run a signal ground with RS-422
|
Typical Data rates: |
115,200 bps (10Mbps over short distances) |
|
Max Distance: |
4000 feet |
|
Cabling Requirements: |
2 twisted pair (1 TD, 1 RD) plus signal ground |
|
Typical Line Designations |
Line A and Line B |
|
Fan out |
1 transmitter can drive up to 10 receivers |
|
Typical Signal Levels |
Mark: VAB = –5 V, Space: VAB = +5 V (differential) |
|
Signal Logic |
Mark – Line A negative with respect to Line B |