PC912XDP512F0MPVR datasheet(551/1348 Pages) FREESCALE

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Chapter 13 Periodic Interrupt Timer (S12PIT24B4CV1)

MC9S12XDP512 Data Sheet, Rev. 2.21

Freescale Semiconductor

551

13.4

Functional Description

Figure 13-19 shows a detailed block diagram of the PIT module. The main parts of the PIT are status,

control and data registers, two 8-bit down-counters, four 16-bit down-counters and an interrupt/trigger

interface.

Figure 13-19. PIT Detailed Block Diagram

13.4.1

Timer

As shown in Figure 13-1and Figure 13-19, the 24-bit timers are built in a two-stage architecture with four

16-bit modulus down-counters and two 8-bit modulus down-counters. The 16-bit timers are clocked with

two selectable micro time bases which are generated with 8-bit modulus down-counters. Each 16-bit timer

is connected to micro time base 0 or 1 via the PMUX[3:0] bit setting in the PIT Multiplex (PITMUX)

A timer channel is enabled if the module enable bit PITE in the PIT control and force load micro timer

(PITCFLMT) register is set and if the corresponding PCE bit in the PIT channel enable (PITCE) register

is set. Two 8-bit modulus down-counters are used to generate two micro time bases. As soon as a micro

time base is selected for an enabled timer channel, the corresponding micro timer modulus down-counter

will load its start value as speciﬁed in the PITMTLD0 or PITMTLD1 register and will start down-counting.

Whenever the micro timer down-counter has counted to zero the PITMTLD register is reloaded and the

connected 16-bit modulus down-counters count one cycle.

PITMLD0 Register

8-Bit Micro Timer 0

PITCFLMT Register

PITLD0 Register

PITMLD1 Register

8-Bit Micro Timer 1

PITMUX Register

PITFLT Register

PITCNT0 Register

Timer 0

PMUX0

PFLT0

PITTF Register

PITINTE Register

Interrupt /

Hardware

Trigger

Interrupt

Request

PITLD1 Register

PITCNT1 Register

Timer 1

[1]

PFLT1

PITLD2 Register

PITCNT2 Register

Timer 2

[2]

PFLT2

PITLD3 Register

PITCNT3 Register

Timer 3

PMUX3

PFLT3

time-out 0

time-

out 1

time-

out 2

Time-Out 3

PFLMT

[1]

[0]

Trigger Interface

Bus

Clock

PIT_24B4C

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