Programmable Interrupt Timer (PIT)
Functional Description
MC68HC908AB32
—
Rev. 1.0
Technical Data
MOTOROLA
Programmable Interrupt Timer (PIT)
223
13.4.1 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.
Addr.
Register Name
Bit 7
6
5
4
3
2
1
Bit 0
$004B
PIT Status and Control
Register
(PSC)
Read:
POF
POIE
PSTOP
0
0
PPS2
PPS1
PPS0
Write:
0
PRST
Reset:
0
0
1
0
0
0
0
0
$004C
PIT Counter Register High
(PCNTH)
Read:
Bit 15
14
13
12
11
10
9
Bit 8
Write:
Reset:
0
0
0
0
0
0
0
0
$004D
PIT Counter Register Low
(PCNTL)
Read:
Bit 7
6
5
4
3
2
1
Bit 0
Write:
Reset:
0
0
0
0
0
0
0
0
$004E
PIT Counter Modulo
Register High
(PMODH)
Read:
Bit 15
14
13
12
11
10
9
Bit 8
Write:
Reset:
1
1
1
1
1
1
1
1
$004F
PIT Counter Modulo
Register Low
(PMODL)
Read:
Bit 7
6
5
4
3
2
1
Bit 0
Write:
Reset:
1
1
1
1
1
1
1
1
= Unimplemented
Figure 13-2. PIT I/O Register Summary
Содержание MC68HC908AB32
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