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Created: August 1998
Modified: December 2002

RS-422 instead of RS-232

How to do the cable up:

RS-422 uses differential signals instead of the GND-related RS-232 level. As a result you need two wires for transmit and two wires for receive. These are named by A (or minus) and B (or plus). Depending which wire has the higher voltage the value (0 or 1) is given. In the rest state B has a positive voltage compared with A.

A RS-232-cable connects the transmit-output of one device with the receive-input of the other device (and vice versa).

For RS-422 you need two wires for this job. The transmit-output A belongs to the receive-input A and the transmit-output B belongs to the receive-input B. The same goes for the opposite direction. The common mass must be connected also; this last point is often forgotten.

This cable up is known as the same as a three-wire-connection of RS-232. Because of the small dimensions most of the extern converters from RS-422 <-> RS-232 have no further outputs and inputs. In this case only XON/XOFF can be used.

For a hardware handshake (RTS/CTS) four wires must be connected additionally between RTS A/B and CTS A/B.

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