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WDT_A Operation
10.2.5 Fail-Safe Features
The WDT_A provides a fail-safe clocking feature, ensuring the clock to the WDT_A cannot be disabled
while in watchdog mode. This means the low-power modes may be affected by the choice for the WDT_A
clock.
In watchdog mode the WDT_A prevents LPMx.5 because in LPMx.5 the WDT_A cannot operate.
If SMCLK or ACLK fails as the WDT_A clock source, VLOCLK is automatically selected as the WDT_A
clock source.
When the WDT_A module is used in interval timer mode, there are no fail-safe features.
10.2.6 Operation in Low-Power Modes
The devices have several low-power modes. Different clock signals are available in different low-power
modes. The requirements of the application and the type of clocking that is used determine how the
WDT_A should be configured. For example, the WDT_A should not be configured in watchdog mode with
a clock source that is originally sourced from DCO, XT1 in high-frequency mode, or XT2 via SMCLK or
ACLK if the user wants to use low-power mode 3. In this case, SMCLK or ACLK would remain enabled,
increasing the current consumption of LPM3. When the watchdog timer is not required, the WDTHOLD bit
can be used to hold the WDTCNT, reducing power consumption.
Any write operation to WDTCTL must be a word operation with 05Ah (WDTPW) in the upper byte (see
Example 10-1. Writes to WDTCTL
; Periodically clear an active watchdog
MOV #WDTPW+WDTCNTCL,&WDTCTL
;
; Change watchdog timer interval
MOV #WDTPW+WSSEL,&WDTCTL
;
; Stop the watchdog
MOV #WDTPW+WDTHOLD,&WDTCTL
;
; Change WDT to interval timer mode, clock/8192 interval
MOV #WDTPW+WWWDTIS0,&WDTCTL
331
SLAU272C – May 2011 – Revised November 2013
Watchdog Timer (WDT_A)
Copyright © 2011–2013, Texas Instruments Incorporated