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Periodic Interrupt Timer (PIT)
PXN20 Microcontroller Reference Manual, Rev. 1
22-8
Freescale Semiconductor
22.4
Functional Description
The PIT block has eight timers for general-purpose use. Each timer can be used to generate trigger pulses
as well as to generate interrupts. Each interrupt is available on a separate interrupt line.
22.4.1
Timers
The timers generate triggers at periodic intervals, when enabled. They load their start values, as specified
in their LDVAL
n
registers, then count down until they reach 0. Then they load their respective start value
again. Each time a timer reaches 0, it will generate a trigger pulse, and set the interrupt flag.
All interrupts can be enabled or masked (by setting the TIE bits in the TCTRL
n
registers). A new interrupt
can be generated only after the previous one is cleared.
If desired, the current counter value of the timer can be read via the CVAL
n
registers.
The counter period can be restarted by first disabling and then re-enabling the timer, using the TEN bit (see
).
The counter period of a running timer can be modified, by first disabling the timer, setting a new load value
and then enabling the timer again (see
It is also possible to change the counter period without restarting the timer by writing the LDVAL
n
register
with the new load value. This value will then be loaded after the next trigger event (see
Figure 22-7. Stopping and Starting a Timer
Figure 22-8. Modifying Running Timer Period
p1
p1
Timer Enabled
Disable
Timer
p1
Start Value = p1
Trigger
Event
p1
Re-Enable
Timer
p1
Timer Enabled
Disable
Timer,
Start Value = p1
Trigger
Event
Re-Enable
Timer
p1
Set new
Start Value
p2
p2
p2
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