EIA-423

EIA-423

(communications, standard)

(Formerly "RS-423") An EIA serial line standard which specifies single ended communication. The mechanical connections for this interface are specified by EIA-449. Although it was originally intented as a successor of EIA-232 it is not widely used. The EIA-232 standard has its limits at 20kbps and 1.5m. EIA-423 can have a cable lenght of 1200m, and achieve a data rate of 100Kbps. When no data is being transmitted, the serial line is at a logical zero (+3 to +15 Volts). A logical one is represented as a signal level of -15 to -3 Volts. In practise, one often finds signals which switch between nominally +4.5 and +0.5 Volts. Such signals are large by modern standards, and because the impedance of the circuits is relatively high, the allowable bit rate is modest. The data is preceded by a start bit which is always a logical one. There may be seven or eight bits of data, possibly followed by an even or odd parity bit and one or two stop bits. A "break" condition is a continuous logical one on the line which is what would be observed if nothing was connected.

Comparing EIA-422, 423, 449 to RS-232-C. Details on RS-232, 422, 423 and 485.

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RS-422

A TIA/EIA standard for serial interfaces that extends distances and speeds beyond RS-232. RS-422 is a balanced system requiring more wire pairs than its RS-423 counterpart and is intended for use in multipoint lines. Both use either a 37-pin connector defined by RS-449 or a 25-pin connector defined by RS-530.

RS-449 and RS-530 specify the pin definitions for RS-422 and RS-423. RS-422/423 specify electrical and timing characteristics. See RS-530.

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