digital counter

(electronics) A discrete-state device (one with only a finite number of output conditions) that responds by advancing to its next output condition.

An instrument which, in its simplest form, provides an output that corresponds to the number of pulses applied to its input. Counters may be categorized into two types: the Moore machine or the Mealy machine. The simpler counter type, the Moore machine, has a single count input (also called the clock input or pulse input), while the Mealy machine has additional inputs that alter the count sequence. Digital counters take many forms, including geared mechanisms (tape counters and odometers are examples), relays (old pinball machines and old telephone switching systems), vacuum tubes (old test equipment), and solid-state semiconductor circuits (most modern electronic counters).

Most digital counters operate in the binary number system, since binary is easily implemented with electronic circuitry. Binary allows any integer (whole number) to be represented as a series of binary digits, or bits, where each bit is either a 0 or 1 (off or on, low or high, and so forth).

Digital counters are found in much modern electronic equipment, especially equipment that is digitally controlled or has digital numeric displays. A frequency counter, as a test instrument or a channel frequency display on a radio tuner, consists simply of a string of decade counters that count the pulses of an input signal for a known period of time, and display that count on a seven-segment display. A digital voltmeter operates by using nearly the same idea, except that the counter counts a known frequency for a period of time proportional to the input voltage. See also Analog-to-digital converter.

A digital watch contains numerous counter/dividers in its large-scale integration (LSI) chip, usually implemented with complementary metal oxide semiconductor (CMOS) technology.

Digital computers may contain counters in the form of programmable interval timers that count an integral number of clock pulses of known period, and then generate an output at the end of the count to signal that the time period has expired. Most of the counters in a microprocessor consist of arithmetic logic units that add one many-bit number to another, storing the results in a memory location. The program and data counters are examples of this kind of counter. See also Digital computer; Microprocessor.

Counters have progressed from relays to light-wavelength-geometry very-large-scale-integrated circuits. There are several technologies for building individual digital counters. Single counters are available as integrated circuit chips in emitter-coupled logic, transistor-transistor logic, and CMOS.