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Pulse dialing

Pulse dialing, also called Rotary or Decadic dialling in UK, (because up to 10 pulses are sent), is Pulsing in which a direct-current pulse train is produced by interrupting a steady signal according to a fixed or formatted code for each digit and at a standard pulse repetition rate.

Dial pulsing originated with a rotary dial integrated into telephone instruments, for the purpose of signaling. Subsequent applications use electronic circuits to generate dial pulses. Synonym pulsing.

Because the pulses are generated through the making and breaking of the telephone connection (akin to flicking a light switch on and off), all that is really needed to dial a number with pulse dialing is a switch (ie. the telephone receiver button). Each number is represented by a series of rapid clicks to the appropriate value (one click for 1, two clicks for 2, etc.) except 0 which has ten clicks. Individual digits in a phone number need to be separated with a short pause so as not to bleed into each other, and in keypad based pulse dialing, digits need to be 'cached' when dialed rapidly -- in rotary systems the user must wait for the rotor to turn back to the correct position before the next digit can be dialed.

Modern phones increasingly use dual tone multi frequency (also called touch tone or tone dialing) rather than pulse dialing.

See also: Federal Standard 1037C