ST7LITE25F2 datasheet(71/166 Pages) STMICROELECTRONICS

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ST7LITE20F2 ST7LITE25F2 ST7LITE29F2

On-chip peripherals

Doc ID 8349 Rev 5

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On-chip peripherals

11.1

Watchdog timer (WDG)

11.1.1

Introduction

The Watchdog timer is used to detect the occurrence of a software fault, usually generated

by external interference or by unforeseen logical conditions, which causes the application

program to abandon its normal sequence. The Watchdog circuit generates an MCU reset on

expiry of a programmed time period, unless the program refreshes the counter’s contents

before the T6 bit becomes cleared.

11.1.2

Main features

●

Programmable free-running downcounter (64 increments of 16000 CPU cycles)

●

Programmable reset

●

Reset (if watchdog activated) when the T6 bit reaches zero

●

Optional reset on HALT instruction (configurable by option byte)

●

Hardware Watchdog selectable by option byte.

11.1.3

Functional description

The counter value stored in the CR register (bits T[6:0]), is decremented every 16000

machine cycles, and the length of the time-out period can be programmed by the user in 64

increments.

If the watchdog is activated (the WDGA bit is set) and when the 7-bit timer (bits T[6:0]) rolls

over from 40h to 3Fh (T6 becomes cleared), it initiates a reset cycle pulling low the reset pin

for typically 30

μs.

Figure 33. Watchdog block diagram

Reset

WDGA

7-bit downcounter

fCPU

Clock divider

Watchdog control register (CR)

÷16000

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