ATTINY817-MFR. datasheet(134/492 Pages) MICROCHIP

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19.

WDT - Watchdog Timer

19.1

Features

•

Issues a System Reset if the Watchdog Timer is not cleared before its timeout period

•

Operating asynchronously from system clock using an independent oscillator

•

Using the 1KHz output of the 32KHz Ultra Low Power oscillator (OSCULP32K)

•

11 selectable timeout periods, from 8ms to 8s

•

Two operation modes:

–

Normal Mode

–

Window Mode

•

Configuration lock to prevent unwanted changes

•

Closed period timer activation after first WDT instruction for easy setup

19.2

Overview

The Watchdog Timer (WDT) is a system function for monitoring correct program operation. It allows to

recover from situations such as runaway or deadlocked code, by issuing a Reset. When enabled, the

WDT is a constantly running timer configured to a predefined timeout period. If the WDT is not reset

within the timeout period, it will issue a System Reset. The WDT is reset by executing the WDR (Watchdog

Timer Reset) instruction from software.

The WDT has two modes of operation, Normal mode and Window mode. The settings in the Control A

A window mode allows to define a time slot or "window" inside the timeout period during which the WDT

must be reset. If the WDT is reset outside this window, either too early or too late, a System Reset will be

issued. Compared to the normal mode, the window mode can also catch situations where a code error

causes constant WDR execution.

When enabled, the WDT will run in active mode and all sleep modes. It is asynchronous, i.e. running from

a CPU-independent clock source. For this reason it will continue to operate and be able to issue a

System Reset even if the main clock fails.

The Configuration Change Protection mechanism ensures that the WDT settings cannot be changed by

accident. For increased safety, a configuration for locking the WDT settings is also available.

ATTINY817-MFR. Datasheet(PDF) 134 Page - Microchip Technology