A Made IT project
RS422 is a balanced serial interface for the transmission of digital data. The advantage of a balanced signal is the greater immunity to noise. The EIA describes RS422 as a DTE to DCE interface for point-to-point connections.
The data is coded as a differential voltage between the wires. The wires are named A (negative) and B (positive). When B > A then the output is a mark (1 or off) and when A > B then it is counted as a space (0 or on).
In general a mark is +1 Vdc for the A line and +4 Vdc for the B line.
A space is +1 Vdc for the B line and +4Vdc for the A line.
At the transmitter end the voltage difference should not be less than 1.5 Vdc and not exceed 5 Vdc.
At the receiver end the voltage difference should not be less than 0.2 Vdc. The minimum voltage level is -7 Vdc and maximum +12 Vdc.
|Max. Distance @ Rate||1200 meter/ 4000 feet @ max. 100 kbps|
|Max. Rate @ Distance||10 Mbps @ 12 meter/ 50 ft|
|Driver Output Resistance||100 ohm|
|Receiver Input Resistance||4 kohm min.|
|Max. Output Current||150 mA|
The interface is normally terminated on a 4 wire screw block or on a Sub-D37 (RS449), but other interfaces are not uncommon.