ATTINY817-MFR. datasheet(137/492 Pages) MICROCHIP

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Figure 19-2. Normal Mode Operation

t [ms]

WDT Count

Timely WDT Reset (WDR)

TOWDT

WDT Timeout

System Reset

TO WDT = 16ms

Here:

Normal mode is enabled as long as the WINDOW bit field in the Control A register (WDT.CTRLA) is 0x0.

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19.3.2.2 Window Mode

In window mode operation, the WDT uses two different timeout periods, a "closed" window timeout period

(TOWDTW) and the normal timeout period (TOWDT):

The closed window timeout period defines a duration from 8ms to 8s where the WDT cannot be reset. If

the WDT is reset during this period, the WDT will issue a System Reset.

The normal WDT timeout period, which is also 8ms to 8s, defines the duration of the "open" period during

which the WDT can (and should) be reset. The open period will always follow the closed period, so the

total duration of the timeout period is the sum of the closed window and the open window timeout periods.

When enabling window mode or when going out of debug mode, the first closed period is activated after

the first WDR instruction.

If a second WDR is issued while a previous WDR is being synchronized, the second one will be ignored.

Figure 19-3. Window Mode Operation

t [ms]

WDT Count

Timely WDT Reset (WDR)

TOWDTW

TOWDT

System Reset

WDR too early:

TOWDTW =TOWDT = 8ms

Here:

The window mode is enabled by writing a non-zero value to the WINDOW bit field in the Control A

19.3.2.3 Configuration Protection and Lock

The WDT provides two security mechanisms to avoid unintentional changes to the WDT settings:

ATtiny417/817

Datasheet Complete

DS40001901B-page 137

ATTINY817-MFR. Datasheet(PDF) 137 Page - Microchip Technology