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15.2.5 Scratch Registers
The RTC provides three general-purpose registers (SCRATCHx_REG) that can be used to store 32-bit
words -- these registers have no functional purpose for the RTC. Software using the RTC may find the
SCRATCHx registers to be useful in indicating RTC states. For example, the SCRATCHx_REG
registers may be used to indicate write-protection lock status or unintentional power downs. To indicate
write-protection, the software should write a unique value to one of the SCRATCHx_REG registers
when write-protection is disabled and another unique value when write-protection is enabled again. In
this way, the lock-status of the registers can be determined quickly by reading the SCRATCH register.
To indicate unintentional power downs, the software should write a unique value to one of the
SCRATCHx_REG registers when RTC is configured and enabled. If the RTC is unintentionally powered
down, the value written to the SCRATCH register is cleared. For more information, see the registers
section.
15.2.6 Power Management
The RTC supports the power idle protocol. It has two SWakeup ports: one for the alarm event and one
for a timer event.
When the RTC is in IDLE mode, the OCP clock is turned off and the 32 kHz clock remains on. The time
and calendar continue to count in IDLE mode. When the RTC is placed back in FUNCTIONAL mode,
the TC registers can be read.
The Alarm SWakeup event can be used to wakeup the RTC when it is in IDLE state. In order to do so,
the alarm needs to be set and enabled before RTC enters the IDLE state. Once this is done, the
SWakeup will occur when the alarm event triggers.
NOTE: Since SWakeup is not periodic, using it to wake up the RTC when in IDLE state is not
recommended. Please use Alarm SWakeup instead.
15.2.7 Reset Considerations
When the device is initially powered on, the RTC may issue spurious interrupt signals to the CPU. To
avoid issues, a software reset should be performed on the RTC module before the CPU interrupt
controller is initialized. Also, see the register summary table in the registers section for reset states of
each register.
SPRUGX9 – 15 April 2011
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Preliminary
© 2011, Texas Instruments Incorporated
Architecture
1543
Real-Time Clock (RTC)
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