SC312XDP512F0MPVR datasheet(552/1348 Pages) FREESCALE

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Chapter 13 Periodic Interrupt Timer (S12PIT24B4CV1)

MC9S12XDP512 Data Sheet, Rev. 2.21

552

Freescale Semiconductor

Whenever a 16-bit timer counter and the connected 8-bit micro timer counter have counted to zero, the

PITLD register is reloaded and the corresponding time-out ﬂag PTF in the PIT time-out ﬂag (PITTF)

micro timer load (PITMTLD) registers and the bus clock fBUS:

time-out period = (PITMTLD + 1) * (PITLD + 1) / fBUS.

For example, for a 40 MHz bus clock, the maximum time-out period equals:

256 * 65536 * 25 ns = 419.43 ms.

The current 16-bit modulus down-counter value can be read via the PITCNT register. The micro timer

down-counter values cannot be read.

The 8-bit micro timers can individually be restarted by writing a one to the corresponding force load micro

timer PFLMT bits in the PIT control and force load micro timer (PITCFLMT) register. The 16-bit timers

can individually be restarted by writing a one to the corresponding force load timer PFLT bits in the PIT

forceload timer (PITFLT) register. If desired, any group of timers and micro timers can be restarted at the

same time by using one 16-bit write to the adjacent PITCFLMT and PITFLT registers with the relevant

bits set, as shown in Figure 13-20.

Figure 13-20. PIT Trigger and Flag Signal Timing

13.4.2

Interrupt Interface

Each time-out event can be used to trigger an interrupt service request. For each timer channel, an

individual bit PINTE in the PIT interrupt enable (PITINTE) register exists to enable this feature. If PINTE

Bus Clock

8-Bit Micro

PITCNT Register

0001

0000

0001

0000

8-Bit Force Load

PTF Flag1

PITTRIG

16-Bit Force Load

0001

0000

0001

Time-Out Period

After Restart

Timer Counter

Note 1. The PTF ﬂag clearing depends on the software

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