Technical Data
MC68HC11E Family
—
Rev. 4
110
Resets and Interrupts
MOTOROLA
Resets and Interrupts
5.3.3 Computer Operating Properly (COP) Reset
The MCU includes a COP system to help protect against software
failures. When the COP is enabled, the software is responsible for
keeping a free-running watchdog timer from timing out. When the
software is no longer being executed in the intended sequence, a
system reset is initiated.
The state of the NOCOP bit in the CONFIG register determines whether
the COP system is enabled or disabled. To change the enable status of
the COP system, change the contents of the CONFIG register and then
perform a system reset. In the special test and bootstrap operating
modes, the COP system is initially inhibited by the disable resets (DISR)
control bit in the TEST1 register. The DISR bit can subsequently be
written to 0 to enable COP resets.
The COP timer rate control bits CR[1:0] in the OPTION register
determine the COP timeout period. The system E clock is divided by 2
15
and then further scaled by a factor shown in
Table 5-1
. After reset, these
bits are 0, which selects the fastest timeout period. In normal operating
modes, these bits can be written only once within 64 bus cycles after
reset.
Table 5-1. COP Timer Rate Select
CR[1:0]
Divide
E/2
15
By
XTAL = 4.0 MHz
Timeout
–
0 ms, + 32.8 ms
XTAL = 8.0 MHz
Timeout
–
0 ms, + 16.4 ms
XTAL = 12.0 MHz
Timeout
–
0 ms, + 10.9 ms
XTAL = 16.0 MHz
Timeout
–
0 ms, + 8.2 ms
0 0
1
32.768 ms
16.384 ms
10.923 ms
8.19 ms
0 1
4
131.072 ms
65.536 ms
43.691 ms
32.8 ms
1 0
16
524.28 ms
262.14 ms
174.76 ms
131 ms
1 1
64
2.098 s
1.049 s
699.05 ms
524 ms
E =
1.0 MHz
2.0 MHz
3.0 MHz
4.0 MHz