18.8.3 Control


Bit	15	14	13	12	11	10	9	8
					PRESCALER[3:0]
Access					R/W	R/W	R/W	R/W
Reset					0	0	0	0


Bit	7	6	5	4	3	2	1	0
	MATCHCLR	CLKREP			MODE[1:0]		ENABLE	SWRST
Access	R/W	R/W			R/W	R/W	R/W	W
Reset	0	0			0	0	0	0

Bits 11:8 – PRESCALER[3:0] Prescaler

These bits define the prescaling factor for the RTC clock source (GCLK_RTC) to generate the counter clock (CLK_RTC_CNT).

These bits are not synchronized.


PRESCALER[3:0]	Name	Description
0x0	DIV1	CLK_RTC_CNT = GCLK_RTC/1
0x1	DIV2	CLK_RTC_CNT = GCLK_RTC/2
0x2	DIV4	CLK_RTC_CNT = GCLK_RTC/4
0x3	DIV8	CLK_RTC_CNT = GCLK_RTC/8
0x4	DIV16	CLK_RTC_CNT = GCLK_RTC/16
0x5	DIV32	CLK_RTC_CNT = GCLK_RTC/32
0x6	DIV64	CLK_RTC_CNT = GCLK_RTC/64
0x7	DIV128	CLK_RTC_CNT = GCLK_RTC/128
0x8	DIV256	CLK_RTC_CNT = GCLK_RTC/256
0x9	DIV512	CLK_RTC_CNT = GCLK_RTC/512
0xA	DIV1024	CLK_RTC_CNT = GCLK_RTC/1024
0xB-0xF		Reserved

Bit 7 – MATCHCLR Clear on Match

This bit is valid only in Mode 0 and Mode 2. This bit can be written only when the peripheral is disabled.

This bit is not synchronized.

Value	Description
0	The counter is not cleared on a Compare/Alarm 0 match.
1	The counter is cleared on a Compare/Alarm 0 match.

Bit 6 – CLKREP Clock Representation

This bit is valid only in Mode 2 and determines how the hours are represented in the Clock Value (CLOCK) register. This bit can be written only when the peripheral is disabled.

This bit is not synchronized.

Value	Description
0	24 Hour
1	12 Hour (AM/PM)

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
0	The peripheral is disabled or being disabled.
1	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.