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Introduction
1481
SPRUH82C – April 2013 – Revised September 2016
Copyright © 2013–2016, Texas Instruments Incorporated
64-Bit Timer Plus
30.1.5.6 General-Purpose Timer Power Management
The timer can be placed in reduced power modes to conserve power during periods of low activity. The
power management of the peripheral is controlled by the processor Power and Sleep Controller (PSC).
The PSC acts as a master controller for power management for all of the peripherals on the device. For
detailed information on power management procedures using the PSC, see the
Power and Sleep
Controller (PSC)
chapter. The timer can be placed in an idle mode to conserve power when it is not being
used.
30.1.6 Architecture – Watchdog Timer Mode
This section describes the use of the timer as a watchdog timer. In order to fully function in watchdog
timer mode, the timer must be internally connected to the device hardware reset signal. For information on
which timer instantiation can function as a watchdog timer, see your device-specific data manual.
30.1.6.1 Watchdog Timer
As a 64-bit watchdog timer, the peripheral can be used to prevent system lockup when the software
becomes trapped in loops with no controlled exit.
After a hardware reset, the watchdog timer is disabled. The timer then can be configured as a watchdog
timer using the timer mode (TIMMODE) bit in the timer global control register (TGCR) and the watchdog
timer enable (WDEN) bit in the watchdog timer control register (WDTCR). In the watchdog timer mode, the
timer requires a special service sequence to be executed periodically. Without this periodic servicing, the
timer counter increments until it matches the timer period and causes a watchdog timeout event.
When the timeout event occurs, the watchdog timer resets the entire processor.
30.1.6.2 Watchdog Timer Mode Restrictions
The watchdog timer mode has the following restrictions:
•
No external clock source
•
No one-time enabling
30.1.6.3 Watchdog Timer Mode Operation
The watchdog timer mode is selected and enabled when:
•
TIMMODE = 2h in TGCR
•
WDEN = 1 in WDTCR
shows the timer when it is used in the watchdog timer mode. The counter registers (TIM12
and TIM34) form a 64-bit timer counter register and the period registers (PRD12 and PRD34) form a 64-bit
period register. When the timer counter matches the timer period, the timer generates a watchdog timeout
event which resets the entire processor.
To activate the watchdog timer, a certain sequence of events must be followed, as shown in the state
diagram of
Once the watchdog timer is activated, it can be disabled only by a watchdog timeout event or by a
hardware reset. A special key sequence is required to prevent the watchdog timer from being accidentally
serviced while the software is trapped in a loop or by some other software failure.
To prevent a watchdog timeout event, the timer has to be serviced periodically by writing A5C6h followed
by DA7Eh to the watchdog timer service key (WDKEY) bits in WDTCR before the timer finishes counting
up. Both A5C6h and DA7Eh are allowed to be written to the WDKEY bits, but only the correct sequence of
A5C6h followed by DA7Eh to the WDKEY bits services the watchdog timer. Any other writes to the
WDKEY bits triggers the watchdog timeout event immediately.
When the watchdog timer is in the Timeout state, the watchdog timer is disabled, the WDEN bit is cleared
to 0, and the timer is reset.