Since the use of RS-232-C has been basically universal since its publication by the EIA in 1969,wewill examine both revisionsCandDinthis section, denoting the differences between the revisions when appropriate. When both revisions are similar, we will refer to them as RS-232-C/D.

In general, devices built to either standard as well as the equivalent ITU-T V.24 recommendation are compatible with one another. There are some slight differences that can occur due to the addition of signals to support modem testing under RS-232-D.

Since the RS-232-C/D standards define the most popular method of interfacing between DTEs and DCEs in the United States, they govern, as an example, the interconnection of most terminal devices to stand-alone modems.

The RS-232-C/D standards apply to series data transfers between a DTE and DCE in the range from0 to 19 200 bits per second. Although the standards also limit the cable length between the DTE and DCE to 50 feet, since the pulse width of digital data is inversely proportional to the data rate, one can normally exceed this 50 foot limitation at lower data rates, as wider pulses are less susceptible to distortion than narrower pulses.

When a cable length in excess of 50 feet is required, it is highly recommended that low capacitance shielded cable be used and tested prior to going on-line, to ensure that the signal quality is acceptable.

Another part of the RS-232-D standard specifies the cable heads that serve as connectors to the DTEs and DCEs. Here the connector is known as a DB-25 connector and each end of the cable is equipped with this ‘male’ connector that is designed to be inserted into the DB-25 female connectors normally built into modems. 

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