MC908AZ32ACFUE Datasheet, PDF (226/324 Pages) Freescale Semiconductor, Inc – Microcontrollers

Programmable Interrupt Timer (PIT)
POF — PIT Overflow Flag Bit
This read/write flag is set when the PIT counter resets to $0000 after reaching the modulo value
programmed in the PIT counter modulo registers. Clear POF by reading the PIT status and control
register when POF is set and then writing a logic 0 to POF. If another PIT overflow occurs before the
clearing sequence is complete, then writing logic 0 to POF has no effect. Therefore, a POF interrupt
request cannot be lost due to inadvertent clearing of POF. Reset clears the POF bit. Writing a logic 1
to POF has no effect.
1 = PIT counter has reached modulo value
0 = PIT counter has not reached modulo value
POIE — PIT Overflow Interrupt Enable Bit
This read/write bit enables PIT overflow interrupts when the POF bit becomes set. Reset clears the
POIE bit.
1 = PIT overflow interrupts enabled
0 = PIT overflow interrupts disabled
PSTOP — PIT Stop Bit
This read/write bit stops the PIT counter. Counting resumes when PSTOP is cleared. Reset sets the
PSTOP bit, stopping the PIT counter until software clears the PSTOP bit.
1 = PIT counter stopped
0 = PIT counter active
NOTE
Do not set the PSTOP bit before entering wait mode if the PIT is required
to exit wait mode.
PRST — PIT Reset Bit
Setting this write-only bit resets the PIT counter and the PIT prescaler. Setting PRST has no effect on
any other registers. Counting resumes from $0000. PRST is cleared automatically after the PIT
counter is reset and always reads as logic zero. Reset clears the PRST bit.
1 = Prescaler and PIT counter cleared
0 = No effect
NOTE
Setting the PSTOP and PRST bits simultaneously stops the PIT counter at
a value of $0000.
PPS[2:0] — Prescaler Select Bits
These read/write bits select one of the seven prescaler outputs as the input to the PIT counter as Table
20-2 shows. Reset clears the PPS[2:0] bits.
Table 20-2. Prescaler Selection
PPS[2:0]
000
001
010
011
100
101
110
111
PIT Clock Source
Internal Bus Clock ÷1
Internal Bus Clock ÷ 2
Internal Bus Clock ÷ 4
Internal Bus Clock ÷ 8
Internal Bus Clock ÷ 16
Internal Bus Clock ÷ 32
Internal Bus Clock ÷ 64
Internal Bus Clock ÷ 64
MC68HC908AZ32A Data Sheet, Rev. 2
226
Freescale Semiconductor