MC68332ACEH20 Datasheet, PDF (22/88 Pages) Freescale Semiconductor, Inc – 32-Bit Modular Microcontroller

Freescale Semiconductor, Inc.
3.2.7 Periodic Interrupt Timer
The periodic interrupt timer (PIT) generates interrupts of specified priorities at specified intervals. Timing
for the PIT is provided by a programmable prescaler driven by the system clock.
PICR — Periodic Interrupt Control Register
$YFFA22
15
14
13
12
11
10
8
7
0
0
0
0
0
0
PIRQL
PIV
RESET:
0
0
0
0
0
0
0
0
0
0
0
0
1
1
1
1
This register contains information concerning periodic interrupt priority and vectoring. Bits [10:0] can be
read or written at any time. Bits [15:11] are unimplemented and always return zero.
PIRQL[2:0] — Periodic Interrupt Request Level
The following table shows what interrupt request level is asserted when a periodic interrupt is generat-
ed. If a PIT interrupt and an external IRQ signal of the same priority occur simultaneously, the PIT in-
terrupt is serviced first. The periodic timer continues to run when the interrupt is disabled.
PIRQL
000
001
010
011
100
101
110
111
Interrupt Request Level
Periodic Interrupt Disabled
Interrupt Request Level 1
Interrupt Request Level 2
Interrupt Request Level 3
Interrupt Request Level 4
Interrupt Request Level 5
Interrupt Request Level 6
Interrupt Request Level 7
PIV[7:0] — Periodic Interrupt Vector
The bits of this field contain the vector generated in response to an interrupt from the periodic timer.
When the SIM responds, the periodic interrupt vector is placed on the bus.
PITR —Periodic Interrupt Timer Register
$YFFA24
15
14
13
12
11
10
9
8
7
0
0
0
0
0
0
0
0
PTP
PITM
RESET:
0
0
0
0
0
0
0 MODCLK 0
0
0
0
0
0
0
0
The PITR contains the count value for the periodic timer. A zero value turns off the periodic timer. This
register can be read or written at any time.
PTP — Periodic Timer Prescaler Control
0 = Periodic timer clock not prescaled
1 = Periodic timer clock prescaled by a value of 512
The reset state of PTP is the complement of the state of the MODCLK signal during reset.
PITM[7:0] — Periodic Interrupt Timing Modulus Field
This is an 8-bit timing modulus. The period of the timer can be calculated as follows:
PIT Period = [(PITM)(Prescaler)(4)]/EXTAL
where
PIT Period = Periodic interrupt timer period
PITM = Periodic interrupt timer register modulus (PITR[7:0])
EXTAL Frequency = Crystal frequency
Prescale = 512 or 1 depending on the state of the PTP bit in the PITR
MOTOROLA
22
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MC68332
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