MC908AZ32ACFUE Datasheet, PDF (224/324 Pages) Freescale Semiconductor, Inc – Microcontrollers

Programmable Interrupt Timer (PIT)
Register Name
Bit 7
6
5
4
3
Read: POF
0
0
PIT Status and Control Register
(PSC)
Write:
0
POIE PSTOP
PRST
Reset: 0
0
1
0
0
Read: Bit 15
14
13
12
11
PIT Counter Register High
(PCNTH)
Write:
Reset: 0
0
0
0
0
Read: Bit 7
6
5
4
3
PIT Counter Register Low
(PCNTL)
Write:
Reset: 0
0
0
0
0
Read:
PIT Counter Modulo Register High
(PMODH)
Write:
Bit 15
14
13
12
11
Reset: 1
1
1
1
1
Read:
PIT Counter Modulo Register Low
(PMODL)
Write:
Bit 7
6
5
4
3
Reset: 1
1
1
1
1
=Unimplemented
Figure 20-2. PIT I/O Register Summary
2
PPS2
0
10
0
2
0
10
1
2
1
Table 20-1. PIT I/O Register Address Summary
Register
Address
PSC
$004B
PCNTH
$004C
PCNTL
$004D
PMODH
$004E
PMODL
$004F
1
PPS1
0
9
0
1
0
9
1
1
1
Bit 0
PPS0
0
Bit 8
0
Bit 0
0
Bit 8
1
Bit 0
1
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.
MC68HC908AZ32A Data Sheet, Rev. 2
224
Freescale Semiconductor