coun·ter1 / ˈkountər/ • n. 1. a long flat-topped fixture in a store or bank across which business is conducted with customers. ∎ a similar structure used for serving food and drinks in a cafeteria or bar. ∎ a countertop.2. an apparatus used for counting. ∎ a person who counts something, for example votes in an election. ∎ Physics an apparatus used for counting individual ionizing particles or events.3. a small disk used as a place marker or for keeping the score in board games. ∎ a token representing a coin.PHRASES: over the counter by ordinary retail purchase, with no need for a prescription or license: [as adj.] over-the-counter medicines. ∎ (of share transactions) taking place outside the stock exchange system.under the counter (or table) (with reference to goods bought or sold) surreptitiously and typically illegally: certain labs have been peddling this drug under the counter | [as adj.] an under-the-counter deal. coun·ter2 • v. [tr.] speak or act in opposition to. ∎ [intr.] respond to hostile speech or action: “What would you like me to do about it ?” she countered ∎ [intr.] Boxing give a return blow while parrying: he countered with a left hook.• adv. (counter to) in the opposite direction to or in conflict with: some actions by the authorities ran counter to the call for leniency.• adj. responding to something of the same kind, esp. in opposition.See also counter-.• n. 1. [usu. in sing.] a thing that opposes or prevents something else. ∎ an answer to an argument or criticism. ∎ Boxing a blow given while parrying; a counterpunch.2. the curved part of the stern of a ship projecting aft above the waterline.3. Printing the white space enclosed by a letter such as O or c.coun·ter3 • n. the back part of a shoe or boot, enclosing the heel.
A counter whose output is capable of displaying n discrete states before producing an overflow condition can also be called a mod-n counter (or modulo-n counter), since it may be considered to be counting input pulses to a base of n. The value of n is often an integer power of 2. Counters are generally formed by a cascaded series of clocked flip-flops (see cascadable counter), each of which provides a divide-by-two action. For a counter consisting of m flip-flops, the maximum capacity of the counter will be 2m since 2m discrete output states are possible, i.e. n is equal to 2m. These are known as binary counters.
Count lengths of other than integer multiples of two are possible. For example, a decade counter (or mod-10 counter) exhibits 10 separate and distinct states. To achieve this digitally requires a counter having at least four individual flip-flop elements, giving 24 or 16 possible output states; six of these states are prevented from occurring by a suitable arrangement of logic gates around the individual flip-flops. In multimode counters the number, n, of distinct states can be selected by the user.
See also ripple counter, synchronous counter, shift counter, Johnson counter.