TC1796
System Units (Vol. 1 of 2)
Watchdog Timer
User’s Manual
16-5
V2.0, 2007-07
WDT, V2.0
16.4
Watchdog Timer Operation
The following sections describe the registers, the operation, and different modes of the
WDT, as well as the Password Access mechanism.
gives an example for
the operation of the WDT. A rough description of the sequence of events in this figure is
provided here. Refer to the following sections for a detailed explanation.
1. Time-Out Mode is automatically entered after reset. Timer counts with slowest input
clock.
2. Time-Out Mode terminated and Normal Mode is entered by setting ENDINIT to 1.
3. Normal Mode is terminated and Time-Out Mode is entered through a Password
Access to WDT_CON0. The reload value was set to REL_1.
4. Time-Out Mode is terminated and Normal Mode entered again by setting ENDINIT to
1. The reload value WDTREL has been changed to REL_2 and the timer input clock
was set to the fast clock.
Events 3) and 4) constitute a WDT service sequence.
5. The WDT was not serviced and continued to count until overflow. Reset Prewarning
Mode is entered. Timer counts with selected fast input clock. Watchdog operation
cannot be altered or stopped in this mode.
6. Timer continued to count until overflow, generating a WDT reset.
7. Time-Out Mode is automatically entered after reset. Timer counts with slowest input
clock.
8. Time-Out Mode is terminated and Normal Mode is entered again.
Figure 16-2 Example for an Operation Sequence of the WDT
MCT05751
REL_1
REL_2
FFFC
H
FFFF
H
1)
2)
3)
4)
5)
WDT Reset
8)
6)
7)
Time-Out
Mode
Normal
Mode
Time-
Out
Mode
Time-Out
Mode
Prewarning
Mode
Normal
Mode