
MC68HC916X1
MOTOROLA
MC68HC916X1TS/D
25
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 SCIM responds, the periodic interrupt vector is placed on the bus.
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
1 = Periodic timer clock prescaled by a value of 512
0 = Periodic timer clock not prescaled
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
The PIT period can be calculated as follows:
where
PIT Period = Periodic interrupt timer period
PITM[7:0] = Periodic interrupt timer register modulus
fref = Synthesizer reference of external clock input frequency
Prescale = 512 or 1 depending on the state of the PTP bit in PITR
3.4 System Protection
System protection includes a bus monitor, a halt monitor, a spurious interrupt monitor, and a soft-
ware watchdog timer. These functions reduce the number of external components required for a
complete control system. Figure 8 shows the SCIM system protection block diagram.
Table 14 Periodic Interrupt Request Levels
PIRQL
Interrupt Request Level
000
Periodic Interrupt Disabled
001
Interrupt Request Level 1
010
Interrupt Request Level 2
011
Interrupt Request Level 3
100
Interrupt Request Level 4
101
Interrupt Request Level 5
110
Interrupt Request Level 6
111
Interrupt Request Level 7
PITR — Periodic Interrupt Timer Register
$YFFA24
15
14
13
12
11
10
9
8
7
6
5
4
3
2
1
0
PTP
PITM[7:0]
RESET:
0
MODCLK
0
PIT Period
PITM[7:0]
) Prescale
() 4
(
()
f
ref
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Freescale Semiconductor, Inc.
For More Information On This Product,
Go to: www.freescale.com
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