Datasheet

Value Description

The counter is cleared on a Compare/Alarm 0 match.

Bits 3:2 – MODE[1:0] Operating Mode

These bits define the operating mode of the RTC.

These bits are not synchronized.

MODE[1:0] Name Description

0x0 COUNT32 Mode 0: 32-bit Counter

0x1 COUNT16 Mode 1: 16-bit Counter

0x2 CLOCK Mode 2: Clock/Calendar

0x3 Reserved

Bit 1 – ENABLE Enable

Due to synchronization, there is delay from writing CTRL.ENABLE until the peripheral is enabled/

disabled. The value written to CTRL.ENABLE will read back immediately, and the Synchronization Busy

bit in the Status register (STATUS.SYNCBUSY) will be set. STATUS.SYNCBUSY will be cleared when

the operation is complete.

This bit is not enable-protected.

Value Description

The peripheral is disabled or being disabled.

The peripheral is enabled or being enabled.

Bit 0 – SWRST Software Reset

Writing a zero to this bit has no effect.

Writing a one to this bit resets all registers in the RTC, except DBGCTRL, to their initial state, and the

RTC will be disabled.

Writing a one to CTRL.SWRST will always take precedence, meaning that all other writes in the same

write-operation will be discarded.

Due to synchronization, there is a delay from writing CTRL.SWRST until the reset is complete.

CTRL.SWRST and STATUS.SYNCBUSY will both be cleared when the reset is complete.

This bit is not enable-protected.

Value Description

There is no reset operation ongoing.

The reset operation is ongoing.

SAM D21 Family

RTC – Real-Time Counter

Datasheet Complete

DS40001882D-page 269