Rainbow-electronics ATmega8515L Bedienungsanleitung PDF herunterladen (Seite 48)

ATmega8515(L)

2512A–AVR–04/02

Figure 27. Watchdog Timer

Watchdog Timer Control

• Bits 7..5 – Res: Reserved Bits

These bits are reservedbits in the ATmega8515 andwill always read aszero.

• Bit 4 – WDCE: Watchdog Change Enable

Thisbit must be set when the WDE bit iswritten to logiczero. Otherwise, the Watchdog

will not be disabled. Once writtentoone,hardware will clear thisbit afterfourclock

cycles.Refer to the description of the WDE bit for a Watchdog disable procedure. In

SafetyLevels 1and 2, thisbit mustalso be set when changing the prescalerbits. See

“TimedSequencesforChanging the Configuration of the Watchdog Timer”onpage 50.

• Bit 3 – WDE: Watchdog Enable

When the WDE iswritten to logic one, the Watchdog Timer is enabled, and if the WDE is

written to logiczero, the Watchdog Timerfunction isdisabled. WDE can only be cleared

if the WDCE bit haslogiclevel one. To disable an enabledWatchdog Timer, the follow-

ing proceduremust be followed:

Table 20. WDT Configuration as a Function of the Fuse Settings ofS8515C and

WDTON.

S8515C WDTON

Safety

Level

WDT

Initial

State

How to Disable

the WDT

How to

Change Time-

out

UnprogrammedUnprogrammed 1 Disabled TimedsequenceTimed

sequence

Unprogrammed Programmed 2 Enabled Always enabled Timed

sequence

ProgrammedUnprogrammed 0 Disabled Timedsequence No restriction

Programmed Programmed 2 Enabled Always enabled Timed

sequence

WATCHDOG

OSCILLATOR

Bit 76543 210

– – – WDCE WDE WDP2 WDP1 WDP0 WDTCR

Read/Write R R R R/W R/W R/W R/W R/W

Initial Value00000000

1 2 ... 43 44 45 46 47 48 49 50 51 52 53 ... 222 223

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