Serial Input/Output and Modems
Chapter 14 explained how data in parallel form may be transmitted from and received by a microcomputer. All the lines of a port are simultaneously sending or receiving data. In contrast, the serial mode of data transmission sends bits of data one at a time along a single conductor, as in Fig. 15-1a. A high voltage may appear at one time and a low voltage an instant later, as shown in Fig. 15-1b. If the voltage is high for 1/300 s, in one type of serial data transmission, for example, that signal could mean a 1 and if low it could mean a zero. A high voltage for 1/150 s is interpreted as two 1’s in succession. Instead of a voltage signal, pulses of current and the lack of them could indicate 0’s and 1’s. Sending parallel data requires eight conductor lines, while a rudimentary system transmitting serial data requires only one line plus a ground line.
KeywordsStatus Register Shift Register Telephone Line Asynchronous Communication Acoustic Coupler
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