WDT_A Operation
761
SLAU356I – March 2015 – Revised June 2019
Copyright © 2015–2019, Texas Instruments Incorporated
Watchdog Timer (WDT_A)
17.2.6.3 WDT_A Operation in LPM3 Mode
The WDT_A remains functional in the LPM3 mode of operation. However, it may be used
only in interval
timer mode
. This is because there is no execution activity to handle the watchdog, and a reset during a
LPM3 condition may result in a nondeterministic device state when it returns to active mode. On the other
hand, if the WDT_A is configured as an interval timer, the interval timer event can be used to wake up the
device back to active mode with full state retention, and the interval timer interrupt is processed correctly.
Before invoking the device entry to LPM3 mode, the WDT_A must be configured to use either BCLK or
VLOCLK as the source. If any of the other clock sources are used, the WDT_A may prevent the device
from entering LPM3 mode and the device will consume excess current as a result. Refer to the
Power
Control Manager (PCM)
chapter for more details about the clock handling during entry to low-power
modes.
17.2.6.4 WDT_A Operation in LPM3.5 Mode
The WDT_A remains functional in the LPM3.5 mode of operation. However, it may be used
only in
interval timer mode
. This is because there is no execution activity to handle the watchdog. On the other
hand, if the WDT_A is configured as an interval timer, the interval timer event can be used to wake up the
device back to active mode.
Before invoking the device entry to LPM3.5 mode, the WDT_A must be configured to use either BCLK or
VLOCLK as the source. If any of the other clock sources are used, the WDT_A may prevent the device
from entering LPM3.5 mode and the device will consume excess current as a result. Refer to the
Power
Control Manager (PCM)
chapter for more details about the clock handling during entry to low-power
modes.
Upon exit from LPM3.5 mode to active mode, the device undergoes a reset, but the WDT_A remains
functional and unaffected by the reset. This isolation is carried out through the LOCKBKUP and
LOCKLPM5 bits in the PCM. Refer to the PCM chapter for more details on entering and exiting LPM3.5
mode of operation.
NOTE:
While the WDT_A operation remains unaffected during and after the LPM3.5 mode, the
WDTCTL register is reset due to the subsequent device reset. It is the responsibility of the
application to re-initialize the WDTCTL register to the value prior to LPM3.5 mode entry
before clearing the LOCKBKUP and LOCKLPM5 bits, else the WDT_A operation is affected
by the reset settings of the register.
17.2.6.5 WDT_A Operation in LPM4 and LPM4.5 Modes
The WDT_A functionality is not available in LPM4 and LPM4.5 modes.