Rainbow-electronics Atmega169L Manuel d'utilisateur télécharger pdf (Page 42)

ATmega169V/L

2514A–AVR–08/02

Watchdog Timer The Watchdog Timer is clocked from a separate On-chip Oscillator which runs at

1 MHz. This is the typical value at V

= 5V. See characterization data for typical values

at other V

levels. By controlling the Watchdog Timer prescaler, the Watchdog Reset

interval can be adjusted as shown in Table 21 on page 43. The WDR – Watchdog Reset

– instruction resets the Watchdog Timer. The Watchdog Timer is also reset when it is

disabled and when a Chip Reset occurs. Eight different clock cycle periods can be

selected to determine the reset period. If the reset period expires without another

Watchdog Reset, the ATmega169 resets and executes from the Reset Vector. For tim-

ing details on the Watchdog Reset, refer to Table 21 on page 43.

To prevent unintentional disabling of the Watchdog or unintentional change of time-out

period, two different safety levels are selected by the fuse WDTON as shown in Table

20. Refer to “Timed Sequences for Changing the Configuration of the Watchdog Timer”

on page 44 for details.

Figure 20. Watchdog Timer

Table 20. WDT Configuration as a Function of the Fuse Settings of WDTON

WDTON

Safety

Level

WDT Initial

State

How to Disable the

WDT

How to Change

Time-out

Unprogrammed 1 Disabled Timed sequence Timed sequence

Programmed 2 Enabled Always enabled Timed sequence

WATCHDOG

OSCILLATOR

1 2 ... 37 38 39 40 41 42 43 44 45 46 47 ... 316 317

Pas de commentaire

Rainbow-electronics Atmega169L Manuel d'utilisateur Page 42