s908az32ag2cfue Freescale Semiconductor, Inc, s908az32ag2cfue Datasheet - Page 224

• Manufacturer Part Number: s908az32ag2cfue
• Description: M68hc08 Microcontrollers 8-bit Microcontroller
• Manufacturer: Freescale Semiconductor, Inc

Programmable Interrupt Timer (PIT)
20.4 PIT Counter Prescaler
The clock source can be one of the seven prescaler outputs. The prescaler generates seven clock rates
from the internal bus clock. The prescaler select bits, PPS[2:0], in the status and control register select
the PIT clock source.
The value in the PIT counter modulo registers and the selected prescaler output determines the frequency
of the periodic interrupt. The PIT overflow flag (POF) is set when the PIT counter value rolls over to $0000
after matching the value in the PIT counter modulo registers. The PIT interrupt enable bit, POIE, enables
PIT overflow CPU interrupt requests. POF and POIE are in the PIT status and control register.
20.5 Low-Power Modes
The WAIT and STOP instructions put the MCU in low power-consumption standby modes.
20.5.1 Wait Mode
The PIT remains active after the execution of a WAIT instruction. In wait mode the PIT registers are not
accessible by the CPU. Any enabled CPU interrupt request from the PIT can bring the MCU out of wait
mode.
If PIT functions are not required during wait mode, reduce power consumption by stopping the PIT before
executing the WAIT instruction.
224
PIT Counter Modulo Register High
PIT Counter Modulo Register Low
PIT Status and Control Register
Register Name
PIT Counter Register High
PIT Counter Register Low
(PMODH)
(PMODL)
(PCNTH)
(PCNTL)
(PSC)
Register
Address
Table 20-1. PIT I/O Register Address Summary
Reset:
Reset:
Reset:
Reset:
Reset:
Read:
Read:
Read:
Read:
Read:
Write:
Write:
Write:
Write:
Write:
Figure 20-2. PIT I/O Register Summary
Bit 7
Bit 15
Bit 15
MC68HC908AZ32A Data Sheet, Rev. 2
POF
Bit 7
Bit 7
0
0
0
0
1
1
$004B
PSC
=Unimplemented
POIE
14
14
PCNTH
6
0
0
6
0
1
6
1
$004C
PSTOP
13
13
PCNTL
5
1
0
5
0
1
5
1
$004D
PRST
PMODH
12
12
4
0
0
0
4
0
1
4
1
$004E
11
11
PMODL
3
0
0
0
3
0
1
3
1
$004F
PPS2
10
10
2
0
0
2
0
1
2
1
Freescale Semiconductor
PPS1
1
0
9
0
1
0
9
1
1
1
Bit 0
PPS0
Bit 8
Bit 0
Bit 8
Bit 0
0
0
0
1
1