HC705CT4GRSSLASHD datasheet(43/152 Pages) NXP

43 / 152 page

MC68HC705CT4 — Rev. 2.0

General Release Specification

MOTOROLA

Resets

General Release Specification — MC68HC705CT4

Section 5. Resets

5.1 Contents

5.2

Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .43

5.3

External Reset (RESET). . . . . . . . . . . . . . . . . . . . . . . . . . . . . .43

5.4

Internal Resets . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .46

5.4.1

Power-On Reset (POR). . . . . . . . . . . . . . . . . . . . . . . . . . . .46

5.4.2

Computer Operating Properly Reset (COPR) . . . . . . . . . . .46

5.4.2.1

Resetting the COP . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .46

5.4.2.2

COP During Wait Mode . . . . . . . . . . . . . . . . . . . . . . . . . .47

5.4.2.3

COP During Stop Mode . . . . . . . . . . . . . . . . . . . . . . . . . .47

5.4.2.4

COP Watchdog Timer Considerations . . . . . . . . . . . . . . .47

5.4.2.5

COP Register . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .48

5.4.3

Illegal Address. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .48

5.2 Introduction

The MCU can be reset from four sources: one external input and three

internal restart conditions. The RESET pin is an input with a Schmitt

trigger as shown in Figure 5-1. All the internal peripheral modules will be

reset by the internal reset signal (RST). Refer to Figure 5-2 for reset

timing detail.

5.3 External Reset (RESET)

The RESET pin is the only external source of a reset. This pin is

connected to a Schmitt trigger input gate to provide an upper and lower

threshold voltage separated by a minimum amount of hysteresis. This

external reset occurs whenever the RESET pin is pulled below the lower

threshold and remains in reset until the RESET pin rises above the

upper threshold. This active-low input will generate the RST signal and

Freescale Semiconductor, Inc.

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