Full, Half, and Single Modes
Depending on the mode of the communications line, two devices may be restricted or
completely free as to when they can transmit. There are three transmission modes a com-
munications line can be configured with. They are Simplex A simplex line is one that can communicate in only one direction.
An example of a simplex communications line is a speaker wire.
Half-duplex A duplex line is one that can carry data in two ways. A
half-duplex line is one that can carry data in two directions, but only in one
direction at a time. A CB (citizen’s band) radio is an example of a half-duplex
line—one party must wait until the other party is finished before speaking.
Full-duplex A full-duplex line can carry data into two directions with both
directions flowing simultaneously. A very good example of a full-duplex
communications line is the telephone system.Serial Ports and Connectors
Serial ports and their connectors have been around since the original PCs, when they
were used to connect to modems and early dot matrix printers. Serial ports send data as a
stream of bits that is transmitted one bit after the other in a series. All serial devices, cables,Chapter 19: Ports and Connectors^483
Figure 19-5. Characters bits are sent at the same time in a parallel transmission and one bit at a
time in a serial transmission