Applicability

The limitations of RS-232 are largely eliminated by the balanced line interface. The RS-422 protocol greatly expands the practical possibilities of the serial bus. It provides a mechanism by which serial data can be transmitted over great distances (to 4,000 feet) and at very high speeds (to10 Mbps). This is accomplished by splitting each signal across two separate wires in opposite states, one inverted and one not inverted. The difference in voltage between the two lines is compared by the receiver to determine the logical state of the signal. This wire configuration, called differential data transmission or balanced transmission, is well suited to noisy environments. With RS-232 communication, which is unbalanced transmission and uses only one wire, signal degradation can take place if there is a difference in ground potential between the transmitting and receiving ends of the cable. With balanced transmission, this potential difference will affect both wires equally, and thus not effect their inverse relationship. Twisted pairs of wire, which ensure that neither line is permanently closer to a noise source than the other, are often used to best equalize influences on the two lines. Errors can be caused by high noise levels affecting one side of the receiver to a different extent than the other. To combat this, each receiver is generally grounded.

RS-422 supports multipoint connections whereas RS-423 supports only point-to-point connections.

Responsible Party

Status

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d895d7a1-e3db-44ff-891a-de16ce31969c