RS-423

RS/EIA/TIA-423 is a standard for serial communications. It defines an unbalanced (single-ended) interface, similar to RS-232, with a single, unidirectional sending driver, and allows for up to 10 receivers. It is normally implemented in integrated circuit technology and can also be employed for the interchange of serial binary signals between DTE & DCE.

RS-423 is closely related to the RS-422 standard, both of which used the same overall signaling system, but differed in that 422 had a dedicated return line for every data pin, while 423 used a single return line. Use of a common ground is one weakness of RS-423 (and RS-232): if devices are far enough apart or on separate power systems, the ground will degrade between them and communications will fail, resulting in a condition that is difficult to trace.[1]

RS-423 and RS-422 were originally developed to use the same DB25 connectors as RS-232, but over time the number of pins grew and the mechanical standard was spun off into the RS-449 standard. This produced an unwieldy system that saw almost no use in the market. A later effort, RS-530, returned to the DB25, but by that time a number of custom connections were already widely used. The BBC Micro computer used a 5-pin DIN connector. DEC used it extensively with a Modified Modular Jack connector. This was sometimes called "DEC-423".