RS422 is among the most popular physical interfaces used in encoders of various types. It is quite similar to its ancestor – RS-485 yet there are some differences that are considerable.
In accordance with the TIA / EIA-422 standard, the RS-422 interface is specified for industrial applications with one data bus master to which up to 10 slaves can be connected. It provides transmission at speeds up to 10 Mbps using twisted pair cable, which improves noise immunity and achieves the highest possible range and data transfer rate.
Typical applications for the RS-422 are industrial process automation (chemicals, food processing, paper mills), integrated manufacturing automation (automotive and metal processing), ventilation and air conditioning systems, security systems, motor control and object movement control.
RS-422 is a full duplex interface. Reception and transmission are carried out on two separate pairs of wires. Each pair of wires can only have one transmitter, All RS-422 devices can be connected to a bus controlled by an RS-485 master. Data transmission goes along two lines, A and B, which are twisted pair (two twisted wires).
The principle of differential transmission of one signal is used. The original signal goes through the A wire, the antiphase signal through the B wire. When one wire has a logical 1, the other has a logical 0 and vice versa. This achieves a high immunity to common-mode interference acting equally on both wires. Electromagnetic interference, passing through the section of the communication line, induces the same potential in each wire, while the informative potential difference remains unchanged.