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Architecture
1326
SPRUH82C – April 2013 – Revised September 2016
Copyright © 2013–2016, Texas Instruments Incorporated
Real-Time Clock (RTC)
27.2.7 General-Purpose Scratch Registers
The RTC provides three general-purpose registers (SCRATCH
n
) 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 SCRATCH
n
registers to be useful in indicating RTC states. For example, the SCRATCH
n
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 SCRATCH
n
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 SCRATCH
n
registers when RTC is configured and enabled. If the RTC is unintentionally powered down, the value
written to the SCRATCH register is cleared.
27.2.8 Real-Time Clock Response to Low Power Modes (Idle Configurations)
The device is divided into idle domains that can be programmed to be idle or active. The state of all
domains is called the idle configuration. The RTC runs on its own external clock source and is not affected
by any of the other device idle domains.
27.2.9 Emulation Modes of the Real-Time Clock
The RTC always continues to run regardless of the state (running/halted) of the emulation debugger
software.
27.2.10 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.
As the RTC is configured, the SPLITPOWER bit in the control register (CTRL) should be set.
A software reset is performed on the RTC by setting the SWRESET bit in the oscillator register (OSC).
The software reset applies to all registers except the oscillator (OSC) and kick (KICK
n
R) registers. The
RTC requires three 32.768-kHz reference clocks to pass before RTC registers can be accessed.