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Counter (digital)
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<p>In <a href="/facts/Digital_electronics/3kJcKbkw">digital electronics</a>, a counter is a <a href="/facts/Sequential_logic/Rcs4thlu">sequential logic</a> circuit that counts and stores the number of positive or negative transitions of a <a href="/facts/Clock_signal/9UfTzGHx">clock signal</a>. A counter typically consists of <a href="/facts/Flip-flop_(electronics)/vA99xjM7">flip-flops</a>, which store a value representing the current count, and in many cases, additional logic to effect particular counting sequences, qualify clocks and perform other functions. Each relevant clock transition causes the value stored in the counter to increment or decrement (increase or decrease by one). </p><p>A digital counter is a <a href="/facts/Finite_state_machine/GMusWd0a">finite state machine</a>, with a <i>clock</i> input signal and multiple output signals that collectively represent the state. The state indicates the current count, encoded directly as a <a href="/facts/Binary_number/a6JDSRPs">binary</a> or <a href="/facts/Binary-coded_decimal/dWTaE7ES">binary-coded decimal</a> (BCD) number or using encodings such as one-hot or Gray code. Most counters have a <i>reset</i> input which is used to initialize the count. Depending on the design, a counter may have additional inputs to control functions such as count enabling and parallel data loading. </p><p>Digital counters are categorized in various ways, including by attributes such as modulus and output encoding, and by supplemental capabilities such as data preloading and bidirectional (up and down) counting. Every counter is classified as either synchronous or asynchronous. Some counters, specifically ring counters and Johnson counters, are categorized according to their unique architectures. </p><p>Counters are the most commonly used sequential circuits and are widely used in computers, measurement and control, device interfaces, and other applications. They are implemented as stand-alone <a href="/facts/Integrated_circuit/fjn6vg7C">integrated circuits</a> and as components of larger integrated circuits such as microcontrollers and FPGAs. </p>