MC68HC16Z1CAG16 Datasheet, PDF (134/500 Pages) Freescale Semiconductor, Inc – M68HC16Z Series users manual

Freescale Semiconductor, Inc.
The periodic interrupt timer modulus counter is clocked by one of two signals. When
the PLL is enabled (MODCLK = 1 during reset), f_ref is used with a slow reference os-
cillator; f_ref 128 is used with fast reference oscillator. When the PLL is disabled (MOD-
CLK = 0 during reset), f_ref is used. The value of the periodic timer prescaler (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 MOD-
CLK pin during reset, as shown in Table 5-11. System software can change PTP val-
ue.
Table 5-11 MODCLK Pin and PTP Bit at Reset
MODCLK
0 (External Clock)
1 (Internal Clock)
PTP
1 (÷ 512)
0 (÷ 1)
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 val-
ue 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:
PIT Period = ⁽---^P----^I--^T---^M-----^[--⁷---^:--⁰---^]--⁾---⁽--¹-----ⁱ-^f----^P----^T---^P----_f--⁼_r--_e---_f⁰----^,---⁵---¹----²-----ⁱ-^f---^P----^T----^P-----⁼------¹---⁾---⁽--⁴----⁾-
The following equation calculates the PIT period when a fast reference frequency is
used:
PIT Period = ⁽---¹---²----⁸---⁾---⁽--^P----^I--^T---^M-----^[--⁷---^:--⁰---^]--⁾---⁽--¹-----ⁱ--^f---^P----^T----^P-----⁼-----⁰----^,---⁵---¹----²-----ⁱ-^f---^P----^T----^P------⁼-----¹----⁾--⁽---⁴---⁾-
f_ref
The following equation calculates the PIT period for an externally input clock frequen-
cy on both slow and fast reference frequency devices.
PIT Period = ⁽---^P----^I--^T---^M-----^[--⁷---^:--⁰---^]--⁾---⁽--¹-----ⁱ-^f----^P----^T---^P----_f--_s⁼--_y---_s⁰----^,---⁵---¹----²-----ⁱ-^f---^P----^T----^P-----⁼------¹---⁾---⁽--⁴----⁾-
5.4.7 Interrupt Priority and Vectoring
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 in-
terrupt control register (PICR).
5-28
SYSTEM INTEGRATION MODULE
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M68HC16 Z SERIES
USER’S MANUAL