MC68HC705P9CS datasheet(96/160 Pages) FREESCALE

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Computer Operating Properly Watchdog (COP)

Technical Data

MC68HC705P9 — Rev. 4.0

Computer Operating Properly Watchdog (COP)

MOTOROLA

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:

where

COP timeout period

131 072 cycles

fBUS

---------------------------------------

fBUS

crystal frequency

---------------------------------------------

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