mc68hc916y3 Freescale Semiconductor, Inc, mc68hc916y3 Datasheet - Page 128

• Manufacturer Part Number: mc68hc916y3
• Description: Mc68hc16y3 16 Bit Microcontroller
• Manufacturer: Freescale Semiconductor, Inc

5.4.7 Interrupt Priority and Vectoring
5-20
MOTOROLA
The periodic interrupt timer modulus counter is clocked by one of two signals. When
the PLL is enabled (MODCLK = 1 during reset), f
oscillator; f
(MODCLK = 0 during reset), f
(PTP) bit in the periodic interrupt timer register (PITR) determines system clock
prescaling for the periodic interrupt timer. One of two options, either no prescaling, or
prescaling by a factor of 512, can be selected. The value of PTP is affected by the state
of the MODCLK pin during reset, as shown in Table 5-7. System software can change
PTP value.
Either clock signal selected by the PTP is divided by four before driving the modulus
counter. The modulus counter is initialized by writing a value to the periodic interrupt
timer modulus (PITM[7:0]) field in PITR. A zero value turns off the periodic timer. When
the modulus counter value reaches zero, an interrupt is generated. The modulus
counter is then reloaded with the value in PITM[7:0] and counting repeats. If a new
value is written to PITR, it is loaded into the modulus counter when the current count
is completed.
The following equation calculates the PIT period when a slow reference frequency is
used:
The following equation calculates the PIT period when a fast reference frequency is
used:
The following equation calculates the PIT period for an externally input clock
frequency on both slow and fast reference frequency devices.
Interrupt priority and vectoring are determined by the values of the periodic interrupt
request level (PIRQL[2:0]) and periodic interrupt vector (PIV) fields in the periodic
interrupt control register (PICR).
ref
PIT Period
PIT Period
PIT Period
128 is used with fast reference oscillator. When the PLL is disabled
Table 5-7 MODCLK Pin and PTP Bit at Reset
Freescale Semiconductor, Inc.
For More Information On This Product,
0 (External Clock)
=
1 (Internal Clock)
------------------------------------------------------------------------------------------------------------------------------------ -
=
=
MODCLK
128 PITM[7:0] 1 if PTP = 0, 512 if PTP = 1 4
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PITM[7:0] 1 if PTP = 0, 512 if PTP = 1 4
PITM[7:0] 1 if PTP = 0, 512 if PTP = 1 4
ref
is used. The value of the periodic timer prescaler
1 ( 512)
0 ( 1)
PTP
f
f
f
ref
ref
ref
ref
is used with a slow reference
MC68HC16Y3/916Y3
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