Programmable Interval Timer (PIT) can act as a user configurable timer interrupt source. It works with the free running 16-bit timer and can provide up to a 1µsec resolution. The PIT cannot be started or stopped, it is always running. If the timer value has to be changed, the user has to wait till the PIT reloads itself at the end of the count cycle (when the count expires). The count change is effective only after this point.