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Chapter 15
Watchdog Timer (WDT)
Preliminary User’s Manual U17566EE1V2UM00
15.1.1
Description
The following figure shows a simplified block diagram.
Figure 15-1
Block diagram of the Watchdog Timer
As shown in the figure, the WDCS register controls the running time and the
WDTM register the operating mode.
The running time can be chosen between 2
13
and 2
20
times the period of the
Watchdog Timer clock WDTCLK.
The figure shows also, that the run and mode settings of the WDTM register
are only cleared by SYSRESWDT.
15.1.2
Principle of operation
Before the Watchdog Timer is started, its running time and mode have to be
configured.
The Watchdog Timer has two operating modes:
• Mode 0 (generate non-maskable interrupt NMIWDT)
• Mode 1 (generate reset request RESWDT)
The mode is defined by the bit WDTM.WDTMODE. The mode can only be
changed after SYSRESWDT, that means, after external RESET or Power-On
Clear.
(1)
Watchdog Timer mode 0 (generate non-maskable interrupt NMIWDT)
If WDTM.WDTMODE is 0, the Watchdog Timer is in interrupt-request mode.
This is the default after initialization.
Setting bit WDTM.RUN to 1 starts the counter. Without intervention, the timer
will now run until the specified time has elapsed and then generate the non-
maskable interrupt NMIWDT. After that, the counter is reset to zero and starts
counting again.
WDTCLK
clear
Counter/Timer
Internal bus
Runtime select
or
2
13
Output
control
circuit
RESWDT
NMIWDT
WDCS2 WDCS1 WDCS0
WDCS
RUN
WDTMODE
WDTM
/ WDTCLK
2
14
/ WDTCLK
2
15
/ WDTCLK
2
16
/ WDTCLK
2
17
/ WDTCLK
2
18
/ WDTCLK
2
19
/ WDTCLK
2
20
/ WDTCLK
SYSRES
SYSRESWDT
reset
SYSRESWDT
reset
overflow
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