mc68hc11d0cfn2 Freescale Semiconductor, Inc, mc68hc11d0cfn2 Datasheet - Page 52

• Manufacturer Part Number: mc68hc11d0cfn2
• Description: M68hc11 Microcontrollers
• Manufacturer: Freescale Semiconductor, Inc

Resets, Interrupts, and Low-Power Modes
4.2.3 Computer Operating Properly (COP) Reset
Data Sheet
52
The MCU contains a watchdog timer that automatically times out unless it is
serviced within a specific time by a program reset sequence. If the COP watchdog
timer is allowed to timeout, a reset is generated, which drives the RESET pin low
to reset the MCU and the external system.
In the MC68HC711D3, the COP reset function is enabled out of reset in normal
modes. If the user does not want the COP enabled, he must write a 1 to the
NOCOP bit of the configuration control register (CONFIG) after reset. This bit is
writable only once after reset in normal modes (see
Register
configuration options register (OPTION) allow the user to select one of the four
COP timeout rates.
the COP timeout period for various system clock frequencies.
The sequence for resetting the watchdog timer is:
Both writes must occur in this sequence prior to the timeout, but any number of
instructions can be executed between the two writes.
CR0 CR1
0
0
1
1
Address:
1. Write $55 to the COP reset register (COPRST) to arm the COP timer
2. Write $AA to the COPRST register to clear the COP timer
Reset:
Read:
Write:
Freescale Semiconductor, Inc.
clearing mechanism.
0
1
0
1
Figure 4-1. Arm/Reset COP Timer Circuitry Register (COPRST)
For More Information On This Product,
for more information). Protected control bits (CR1 and CR0) in the
Divided
$003A
E
Bit 7
Bit 7
Resets, Interrupts, and Low-Power Modes
E =
0
By
16
64
1
4
2
15
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–0/+15.6 ms
Table 4-1
XTAL = 2
15.625 ms
Bit 6
Time Out
2.1 MHz
62.5 ms
250 ms
6
0
1 sec
Table 4-1. COP Time Out Periods
23
Bit 5
shows the relationship between CR1 and CR0 and
5
0
–0/+16.4 ms
16.384 ms
65.536 ms
262.14 ms
Time Out
1.049 sec
8.0 MHz
2.0 MHz
XTAL =
Bit 4
4
0
–0/+26.7 ms
4.9152 MHz
1.2288 MHz
26.667 ms
106.67 ms
426.67 ms
Time Out
1.707 sec
XTAL =
Bit 3
3
0
2.3.3 Configuration Control
Bit 2
–0/+32.8 ms
2
0
32.768 ms
131.07 ms
524.29 ms
Time Out
4.0 MHz
1.0 MHz
XTAL =
2.1 sec
MC68HC711D3 — Rev. 2
Bit 1
1
0
–0/+35.6 ms
3.6864 MHz
35.556 ms
142.22 ms
568.89 ms
MOTOROLA
921.6 kHz
Time Out
2.276 ms
XTAL =
Bit 0
Bit 0
0