Jim Elwell wrote: > For example, PC serial ports use the > RS-232 interface. The EIA(RS)-232-D serial standard is still > specified for operation only up to 20,000 baud; PCs surpassed > that a decade ago. You've triggered my nit-picking mode, Jim. <g> The electrical and circuit definition portions of the EIA-232-D (the RS was dropped by the EIA more than 20 years ago) standard are still used for serial interfaces. The originally specified maximum data rate of 20 000 bit/s (not baud, which is one change of state per second for an analog signal [EIA-232-D* is digital]) was the limit only for a cable of a certain length (15 m). Shorter cables don't suffer the same degree of mark/space distortion and can carry much faster signals (well over 100 000 bit/s) without any departure from the electrical specifications of the standard. The standard does, in fact, specify a permissible voltage range for the signals. Use of a voltage at the low end of the range significantly reduces mark/space distortion, allowing data rates to vastly exceed the nominal 20 000 bit/s of the specification, even with a long cable. The electrical portion of EIA 232-D is codified, internationally, as ITU-T V.28. The circuit assignments are defined in ITU-T V.24. Connector standards and pin/circuit assignments are covered by separate standards (e.g., ISO 2110 for the 25-pin D connector) or are de facto (e.g., 9-pin D connector, as used at the PC end of the cable). (9-pin connectors are defined in ISO 4903, although for a different interface type and with different circuit assignments.) * The full name of EIA-232-D is "Interface between data terminal equipment and data circuit-terminating equipment employing serial binary data interchange." Bill Potts, CMS Roseville, CA http://metric1.org [SI Navigator]
