MAC7200 datasheet(554/976 Pages) FREESCALE

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Functional Description

MAC7200 Microcontroller Family Reference Manual, Rev. 2

476

Freescale Semiconductor

26.9

Functional Description

26.9.1

General

This section gives detailed information on the internal operation of the module. The PIT block has 11

timers: one RTI timer especially to wakeup the processor and 10 additional timers for general-purpose use

(e.g. DMA triggering, ATD triggering).

26.9.1.1

Timer / RTI

The timers generate triggers at periodic intervals, when enabled. They load their start values, as specified

in their TLVAL registers, then count down until they reach 0. This creates a trigger then they load their

respective start value again. Each time a timer reachers 0, it will generate a trigger pulse, and set the

interrupt flag.

All interrupts can be enabled or masked (by setting the TIE/RTIE bits in the PITINTEN register and

selecting interrupts in the PITINTSEL register). A new interrupt can be generated only after the previous

one is cleared. Since in the case of the RTI, clearing the interrupt crosses clock domains, a minimum load

value of 32 should be maintained.

If desired, the current counter value of the timer can be read via the TVAL registers. The value of the RTI

counter can be delayed considerably, as it is synchronized to the bus clock from the RTI clock domain.

The counter period can be restarted, by first disabling, then enabling the timer with the PITEN registers

(see Figure 26-11).

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 Figure 26-12).

It is also possible to change the counter period without restarting the timer by writing the TLVAL register

with the new load value. This value will then be loaded after the next trigger event (see Figure 26-13).

Figure 26-11. Stopping and Starting a Timer

Figure 26-12. Modifying Running Timer Period

Timer Enabled

Disable

Timer

Start Value = p1

Trigger

Event

Re-Enable

Timer

Timer Enabled

Disable

Timer,

Start Value = p1

Trigger

Event

Re-Enable

Timer

Set new

Start Value

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