Programmable Interval Timer

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In computing, a Programmable Interval Timer (PIT) is a counter which triggers an interrupt when it reaches the programmed count.

1 Common Features
2 Well Known PITs
3 IBM PC compatible
4 See also

[edit] Common Features

PITs counters may be one-shot or periodic. One-shot timers interrupt only once, and then stop counting. Periodic timers interrupt every time they reach a specific value.

Counters are usually programmed with fixed increment intervals which determine how long the counter counts before it triggers an interrupt. The interval increments therefore determine the resolution for which the counter may be programmed to generate its one-shot or periodic interrupt.

[edit] Well Known PITs

Some of the best known PITs are the Intel 8253 and Intel 8254 family.

[edit] IBM PC compatible

PITs are the oldest timing devices used on IBM PC compatibles. They use a 1.193182 MHz crystal oscillator (one third of NTSC color burst) and contain three timers. Timer 0 is used by Microsoft Windows (uniprocessor) and Linux as a system timer, timer 1 was historically used for RAM refreshes and timer 2 for the PC speaker.