MC9S12XD256MAL Datasheet, PDF (551/1348 Pages) Freescale Semiconductor, Inc – Freescale’s Scalable Controller Area Network

Chapter 13 Periodic Interrupt Timer (S12PIT24B4CV1)
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.
PITFLT Register
4
PFLT0
PMUX0
4
Timer 0
PITLD0 Register
PITMUX Register
PITCNT0 Register
Bus
Clock
PITMLD0 Register
8-Bit Micro Timer 0
[0]
PFLT1
[1]
Timer 1
PITLD1 Register
PITCNT1 Register
PITMLD1 Register
8-Bit Micro Timer 1
[1]
PITCFLMT Register
PFLMT
PMUX3
PFLT2
[2]
Timer 2
PITLD2 Register
PITCNT2 Register
PFLT3
Timer 3
PITLD3 Register
PITCNT3 Register
PIT_24B4C
time-out 0
time-
out 1
Interrupt /
Trigger Interface
time-
out 2
PITTF Register
PITINTE Register
4
Hardware
Trigger
4
Interrupt
Request
Time-Out 3
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)
register.
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.
MC9S12XDP512 Data Sheet, Rev. 2.21
Freescale Semiconductor
551