Freescale Semiconductor, Inc.
Computer Operating Properly Watchdog (COP)
8.3 Introduction
The purpose of the computer operating properly (COP) watchdog is to
reset the MCU in case of software failure. Software that is operating
properly periodically services the COP watchdog and prevents the reset
from occurring. The COP watchdog function is programmable in the
mask option register.
8.4 Operation
8.4.1 COP Watchdog Timeout
The COP watchdog is a 16-bit counter that generates a reset if allowed
to time out. Periodically clearing the counter starts a new timeout period
and prevents the COP from resetting the MCU. A COP watchdog
timeout indicates that the software is not executing instructions in the
correct sequence.
NOTE: The internal clock drives the COP watchdog. Therefore, the COP
watchdog cannot generate a reset for errors that cause the internal clock
to stop.
The COP watchdog also depends on a power supply voltage at or above
a minimum specification and is not guaranteed to protect against
brownout. For information about brownout protection, see Section 5.
Resets and Interrupts.
8.4.2 COP Watchdog Timeout Period
Use the following formula to calculate the COP timeout period:
131,072 cycles
COP timeout period = --------------------------------------
f
BUS
where
crystal frequency
= --------------------------------------------
2
f
BUS
Technical Data
96
MC68HC705P9 — Rev. 4.0
MOTOROLA
Computer Operating Properly Watchdog (COP)
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