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Counters

  Counters are discussed in Wakerly, Section 8.4. A mod-p counter is a sequential system capable of counting in the sequence of numbers

$$0, 1, 2, \ldots, p-1, 0, 1, 2, \ldots, p-1, 0, 1, \ldots$$

For instance, a decimal counter (i.e. mod-10) counts through the sequence

$$0, 1, 2, 3, 4, 5, 6, 7, 8, 9, 0, 1, 2, \ldots$$

and is useful for creating timing circuits.

A useful application is clock frequency division, where chains of mod-p counters can be used to produce clock waveforms of reduced frequencies. E.g. a cascade of two decimal (or decade) counters driven by a 1000 Hz signal can produce (amoung others) waveforms of frequencies 100 Hz and 10 Hz.

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