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RTC_SS
20.3.3.6 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 Section 20.3.5, RTC Registers.
20.3.3.7 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.
20.3.3.8 Power Management—System Level (PMIC Mode)
The RTC genertates pmic_power_en control which can be used to control an external PMIC.
Table 20-62. pmic_power_en Description
Port Direction Function
Not optional.
RTC true power on domain reset.
rtc_pwronrstn Input Only assert when RTC has lost power.
Always de-assert when RTC voltage is greater than Vmin.
The port remains de-asserted during normal operations.
Optional.
Can be used to control an external PMIC.
0 = OFF
1 = ON (reset state)
pmic_power_en Output
ON → OFF (Turn OFF)
By ALARM2 event
OFF → ON (Turn ON)
By ALARM event OR ext_wakeup event
ext_wakeup Input
3631
SPRUH73H–October 2011–Revised April 2013 Timers
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