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EB413

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Motorola Semiconductor Engineering Bulletin

EB413

Resetting MCUs

By Ross Mitchell

MCU Applications

Motorola Ltd.

East Kilbride, Scotland

Introduction

A simple function such as reset can cause many problems since

different applications impose very different conditions on the start up and

power down of the microcontroller unit (MCU). This document covers the

main issues relating to reset and aims to lead the user of the M68HC05

and M68HC11 devices to a safe a reliable approach for the application.

Reset in its most basic function ensures that the MCU starts executing

code in a controlled manner once power is applied. It may also be used

to prevent the device running out of specification (often in conjunction

with external devices) and can cause a system reset at the board level

whenever the MCU has not executed the code in the expected way

(watchdog).

Freescale Semiconductor, Inc.

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