If the EIA232 standard were strictly followed, these signals would have the same name for the same pin number on the DCE side as well.Strangio Copyright 1993-2015 by CAMI Research Inc., Acton, Massachusetts.
![]() It was thought that a standard was needed first to ensure reliable communication, and second to enable the interconnection of equipment produced by different manufacturers, thereby fostering the benefits of mass production and competition. It specified signal voltages, signal timing, signal function, a protocol for information exchange, and mechanical connectors. Over the 40 years since this standard was developed, the Electronic Industries Association published three modifications, the most recent being the EIA232F standard introduced in 1997. Besides changing the name from RS232 to EIA232, some signal lines were renamed and various new ones were defined, including a shield conductor. Standard Serial Cable Pinout Serial Interfaces AreToday, virtually all contemporary serial interfaces are EIA232-like in their signal voltages, protocols, and connectors, whether or not a modem is involved. Because no single simplified standard was agreed upon, however, many slightly different protocols and cables were created that obligingly mate with any EIA232 connector, but are incompatible with each other. Most of the difficulties you will encounter in EIA232 interfacing include at least one of the following. In any case, if the serial interface between two devices is not operating correctly, disconnect the cable joining this equipment until the problem is isolated. Equipment at the near end of the connection (the telephone line interface) is named the DCE device (Data Circuit-terminating Equipment, usually a modem), has a female DB25 connector, and utilizes the same 22 available pins for signals and ground. The cable linking DTE and DCE devices is a parallel straight-through cable with no cross-overs or self-connects in the connector hoods. If all devices exactly followed this standard, all cables would be identical, and there would be no chance that an incorrectly wired cable could be used. This drawing shows the orientation and connector types for DTE and DCE devices. DCE devices are sometimes called Data Communications Equipment instead of Data Circuit-terminating Equipment. For any DCE device that is not a modem, or when two DTE devices are directly linked, far fewer signal lines are necessary. You may have noticed in the pinout drawings that there is a secondary channel which includes a duplicate set of flow-control signals. This secondary channel provides for management of the remote modem, enabling baud rates to be changed on the fly, retransmission to be requested if a parity error is detected, and other control functions. This secondary channel, when used, is typically set to operate at a very low baud rate in comparison with the primary channel to ensure reliability in the control path. In addition, it may operate as either a simplex, half-duplex, or full-duplex channel, depending on the capabilities of the modem. Transmitter and receiver timing signals (pins 15, 17, and 24) are used only for a synchronous transmission protocol. For the standard asynchronous 8-bit protocol, external timing signals are unnecessary.
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