S912XEG384J3VA Datasheet, PDF (687/1324 Pages) Freescale Semiconductor, Inc – MC9S12XEP100 Reference Manual Covers MC9S12XE Family

Chapter 18 Periodic Interrupt Timer (S12PIT24B4CV2)
Table 18-10. PITCNT0–3 Field Descriptions
Field
Description
15:0 PIT Count Bits 15-0 — These bits represent the current 16-bit modulus down-counter value. The read access
PCNT[15:0] for the count register must take place in one clock cycle as a 16-bit access.
18.4 Functional Description
Figure 18-19 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.
Bus
Clock
4
PITFLT Register
4
PITMUX Register
PITMLD0 Register
8-Bit Micro Timer 0
[0]
PITMLD1 Register
8-Bit Micro Timer 1
[1]
PITCFLMT Register
PFLMT
PFLT0
PMUX0
Timer 0
PITLD0 Register
PITCNT0 Register
PFLT1
[1]
Timer 1
PITLD1 Register
PITCNT1 Register
PFLT2
[2]
Timer 2
PITLD2 Register
PITCNT2 Register
PFLT3
[3]
Timer 3
PITLD3 Register
PITCNT3 Register
PIT24B4C
time-out 0
time-out 1
time-
out 3
time-
out 3
Interrupt /
Trigger Interface
PITTF Register
PITINTE Register
4
Hardware
Trigger
4
Interrupt
Request
Figure 18-19. PIT24B4C Detailed Block Diagram
18.4.1 Timer
As shown in Figure 18-1 and Figure 18-19, 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.
MC9S12XE-Family Reference Manual Rev. 1.25
Freescale Semiconductor
687