4 - Serial interfaces

Abstract

Serial interfaces are used to connect signals from the personal computer to data communication equipment or other computers using copper cables. The most common serial interface is RS-232, otherwise known as V.24. This has been used for many years and has been continually enhanced to make sure that it can still provide a valuable function. Most personal computers have at least one RS-232 port. The ITU issued the latest V.24 specification at the end of the year 2000. A number of interface specifications are used where RS-232 is not suitable. The most recent are the universal serial bus (USB) and IEEE-1394 that permits very high data rates over copper cables. These interfaces are described in this chapter. In serial data transmission, one data bit is transmitted after another. In order to transmit a byte of data, it is therefore necessary to convert incoming parallel data from the bus into a serial bit stream that can be transmitted along a line. Serial data transmission can be synchronous or asynchronous. The latter method has obvious advantages and is by far the most popular method. The rate at which data is transmitted is given by the number of bits transmitted per unit time. The commonly adopted unit is the “baud,” with one baud roughly equivalent to one bit per second.