Digital counters are very useful in many applications. They can be easily found in digital clocks and parallel-to-serial data conversion (multiplexing). In this section, we will use the later as an example on how counters are being used.A group of bits appearing simultaneously on parallel lines is called parallel data. A group of bits appearing on a single line in a time sequence is called serial data. Parallel-to-serial conversion is normally accomplished by the use of a counter to provide a binary sequence for the data-select inputs of a multiplexer, as illustrated in the circuit below.
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The Q outputs of the modulus-8 counter are connected to the data-select
inputs of an eight-bit multiplexer. The first byte (eight-bit group)
of parallel data is applied to the multiplexer inputs. As the counter
goes through a binary sequence from 0 to 7, each bit beginning with D0, is
sequentially selected and passed through the multiplexer to the output line.
After eight clock pulses, the data byte has been converted to a serial format and sent out on the transmission line. Then, the counter recycles back to 0 and converts another parallel byte sequentially again by the same process. |
