Atmel Xplained Pro Evaluation Kit for the ATSAMD21J18A Microcontroller ATSAMD21-XPRO ATSAMD21-XPRO Data Sheet
Product codes
ATSAMD21-XPRO
224
Atmel | SMART SAM D21 [DATASHEET]
Atmel-42181C–SAM-D21_Datasheet–07/2014
This results in a resolution of 1.0006PPM.
The Sign bit in the Frequency Correction register (FREQCORR.SIGN) determines the direction of the correction. A
positive value will speed up the frequency, and a negative value will slow down the frequency.
positive value will speed up the frequency, and a negative value will slow down the frequency.
Digital correction also affects the generation of the periodic events from the prescaler. When the correction is applied at
the end of the correction cycle period, the interval between the previous periodic event and the next occurrence may also
be shortened or lengthened depending on the correction value.
the end of the correction cycle period, the interval between the previous periodic event and the next occurrence may also
be shortened or lengthened depending on the correction value.
18.6.5 DMA Operation
Not applicable.
18.6.6 Interrupts
The RTC has the following interrupt sources:
z
Overflow (
.OVF): this is an asynchronous interrupt and can be used to wake-up the device from any
sleep mode.
z
Compare n (
.CMPn): this is an asynchronous interrupt and can be used to wake-up the device from any
sleep mode.
z
.ALARMn): this is an asynchronous interrupt and can be used to wake-up the device from any
sleep mode.
z
Synchronization Ready (
.SYNCRDY): this is an asynchronous interrupt and can be used to wake-up the
device from any sleep mode.
Each interrupt source has an interrupt flag associated with it. The interrupt flag in the Interrupt Flag Status and Clear
register (INTFLAG) is set when the interrupt condition occurs. Each interrupt can be individually enabled by writing a one
to the corresponding bit in the Interrupt Enable Set register (INTENSET), and disabled by writing a one to the
corresponding bit in the Interrupt Enable Clear register (INTENCLR). An interrupt request is generated when the interrupt
flag is set and the corresponding interrupt is enabled. The interrupt request remains active until the interrupt flag is
cleared, the interrupt is disabled or the RTC is reset. See INTFLAG for details on how to clear interrupt flags. The RTC
has one common interrupt request line for all the interrupt sources. The user must read INTFLAG to determine which
interrupt condition is present.
register (INTFLAG) is set when the interrupt condition occurs. Each interrupt can be individually enabled by writing a one
to the corresponding bit in the Interrupt Enable Set register (INTENSET), and disabled by writing a one to the
corresponding bit in the Interrupt Enable Clear register (INTENCLR). An interrupt request is generated when the interrupt
flag is set and the corresponding interrupt is enabled. The interrupt request remains active until the interrupt flag is
cleared, the interrupt is disabled or the RTC is reset. See INTFLAG for details on how to clear interrupt flags. The RTC
has one common interrupt request line for all the interrupt sources. The user must read INTFLAG to determine which
interrupt condition is present.
Note that interrupts must be globally enabled for interrupt requests to be generated. Refer to
18.6.7 Events
The RTC can generate the following output events, which are generated in the same way as the corresponding
interrupts:
interrupts:
z
Overflow (OVF)
z
Period n (PERn)
z
Compare n (CMPn)
z
Alarm n (ALARMn)
Output events must be enabled to be generated. Writing a one to an Event Output bit in the Event Control register
(EVCTRL.xxEO) enables the corresponding output event. Writing a zero to this bit disables the corresponding output
event. Refer to
(EVCTRL.xxEO) enables the corresponding output event. Writing a zero to this bit disables the corresponding output
event. Refer to
18.6.8 Sleep Mode Operation
The RTC will continue to operate in any sleep mode where the source clock is active. The RTC interrupts can be used to
wake up the device from a sleep mode, or the RTC events can trigger other operations in the system without exiting the
sleep mode.
wake up the device from a sleep mode, or the RTC events can trigger other operations in the system without exiting the
sleep mode.