Serial Input/Output and Modems

  • W. F. Stoecker
  • P. A. Stoecker


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.


Status Register Shift Register Telephone Line Asynchronous Communication Acoustic Coupler 
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  1. 1.
    Interface Between Data Terminal Equipment and Data Communication Equipment Employing Serial Binary Interchange, Standard RS-232-C, Catalog 3, Electronic Industrial Association, 2001 Eye Street, NW, Washington, DC 20006.Google Scholar
  2. 2.
    J. E. Oleksy and G. B. Rutkowski, Microprocessor and Digital Computer Technology, Prentice-Hall, Englewood Cliffs, NJ, 1981.Google Scholar
  3. 3.
    J. E. McNamara, Technical Aspects of Data Communication, Digital Press, Bedford, MA, 1977.Google Scholar

Copyright information

© Van Nostrand Reinhold 1989

Authors and Affiliations

  • W. F. Stoecker
    • 1
  • P. A. Stoecker
    • 2
  1. 1.University of IllinoisUrbana-ChampaignUSA
  2. 2.Hewlett-Packard CompanyUSA

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