new RS-422 and RS-423 standards used well-defined grounding that was always based on the sender's reference, and made the signal only 400 mV above or below this reference. In the case of RS-422, for instance, every signal had a second pin operating at the opposite voltage, thereby balancing the voltages and always providing a positive signal. When this process was starting, the decision was made to unbundle the mechanical aspects of the standard from the electrical, with the former becoming the RS-449 standards track. The primary difference between RS-422 and RS-423 was that the former had a return line for every signal, while the later had a single shared signal ground. This meant that RS-422 had double the number of signal wires. Along with other changes, the number of connections began to grow, to the point where even RS-423, which was functionally similar to RS-232, no longer fit in a DB25 connector. This led to the use of the larger DC-37, but even that did not have enough pins to support RS-422, so this was "solved" by adding the additional ground wires to a separate DE-9 connector. This resulted in a "horrendous number of wires" and the conclusion in 1983 that its "success... remains to be seen." The standard was rarely used, although it could be found on some network communication equipment. EIA-449-1 was rescinded in January 1986 and superseded by EIA/TIA-530-A, the final version EIA-449-1 was withdrawn in September 2002. The most widespread use of RS-422/423, the early Apple Macintosh computers, used a simple 9-pin DIN connector and for inter-machine links used only three-wire connectors. See also Electronic Industries Alliance RS-485 USB Apple Desktop Bus Notes References Citations Sources Electronic Industries Association, EIA Standard 449 November 1977, reprinted in Telebyte Technology "Data Communication Library" Greenlawn NY, 1985, no ISBN, no Library of Congress card number External links EIA/TIA Standards RS-449 interface pinout and signals Serial buses Physical layer protocols EIA standards