A counter is a device for recording the number of events, operations, or pulses that have occurred. The counter must keep the total and provide an indication of the total number, or count, that has been handled. Counters may also be used for dividing frequencies, for addressing information in storage, or for temporary storage.
Counters are a series of flip-flops wired together to perform the type of counting desired. They will count up or down by ones, twos, or more.
The total number of counts or stable states a counter can indicate is called modulus. For instance, the modulus of a four-stage counter would be 1610, since it is capable of indicating 00002 to 11112. The term modulo is used to describe the count capability of counters; that is, modulo-16 for a four-stage binary counter, modulo-10 for a decade counter, modulo-8 for a three-stage binary counter, and so forth.