Datasheet

138
Atmel | SMART SAM D20 [DATASHEET]
Atmel-42129K–SAM-D20_datasheet–06/2014
2. Write the selected value to the BOD33.PSEL bit group.
16.6.8.4 Hysteresis
The hysteresis functionality can be used in both continuous and sampling mode. Writing a one to the BOD33 Hysteresis
bit (BOD33.HYST) in the BOD33 register will add hysteresis to the BOD33 threshold level.
16.6.9 Voltage Reference System Operation
The Voltage Reference System (VREF) consists of a Bandgap Reference Voltage Generator and a temperature sensor.
The Bandgap Reference Voltage Generator is factory-calibrated under typical voltage and temperature conditions.
At reset, the VREF.CAL register value is loaded from Flash Factory Calibration.
The temperature sensor can be used to get an absolute temperature in the temperature range of CMIN to CMAX
degrees Celsius. The sensor will output a linear voltage proportional to the temperature. The output voltage and
temperature range are located in the “Electrical Characteristics” on page 563. To calculate the temperature from a
measured voltage, the following formula can be used:
16.6.9.1 User Control of the Voltage Reference System
To enable the temperature sensor, write a one the Temperature Sensor Enable bit (VREF.TSEN) in the VREF register.
The temperature sensor can be redirected to the ADC for conversion. The Bandgap Reference Voltage Generator output
can also be routed to the ADC if the Bandgap Output Enable bit (VREF.BGOUTEN) in the VREF register is set.
The Bandgap Reference Voltage Generator output level is determined by the CALIB bit group (VREF.CALIB) value in the
VREF register.The default calibration value can be overridden by the user by writing to the CALIB bit group.
16.6.10 Interrupts
The SYSCTRL has the following interrupt sources:
z XOSCRDY - Multipurpose Crystal Oscillator Ready: A “0-to-1” transition on the PCLKSR.XOSCRDY bit is detected
z XOSC32KRDY - 32kHz Crystal Oscillator Ready: A “0-to-1” transition on the PCLKSR.XOSC32KRDY bit is detected
z OSC32KRDY - 32kHz Internal Oscillator Ready: A “0-to-1” transition on the PCLKSR.OSC32KRDY bit is detected
z OSC8MRDY - 8MHz Internal Oscillator Ready: A “0-to-1” transition on the PCLKSR.OSC8MRDY bit is detected
z DFLLRDY - DFLL48M Ready: A “0-to-1” transition on the PCLKSR.DFLLRDY bit is detected
z DFLLOOB - DFLL48M Out Of Boundaries: A “0-to-1” transition on the PCLKSR.DFLLOOB bit is detected
z DFLLLOCKF - DFLL48M Fine Lock: A “0-to-1” transition on the PCLKSR.DFLLLOCKF bit is detected
z DFLLLOCKC - DFLL48M Coarse Lock: A “0-to-1” transition on the PCLKSR.DFLLLOCKC bit is detected
z DFLLRCS - DFLL48M Reference Clock has Stopped: A “0-to-1” transition on the PCLKSR.DFLLRCS bit is detected
z BOD33RDY - BOD33 Ready: A “0-to-1” transition on the PCLKSR.BOD33RDY bit is detected
z BOD33DET - BOD33 Detection: A “0-to-1” transition on the PCLKSR.BOD33DET bit is detected
z B33SRDY - BOD33 Synchronization Ready: A “0-to-1” transition on the PCLKSR.B33SRDY bit is detected
Each interrupt source has an interrupt flag associated with it. The interrupt flag in the Interrupt Flag Status and Clear
(INTFLAG) register 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 (INTENSET) register, and disabled by writing a one to the
corresponding bit in the Interrupt Enable Clear (INTENCLR) register. 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 SYSCTRL is reset. See Interrupt Flag Status and Clear (INTFLAG) register for
details on how to clear interrupt flags.
All interrupt requests from the peripheral are ORed together on system level to generate one combined interrupt request
to the NVIC. Refer to “Nested Vector Interrupt Controller” on page 25 for details. The user must read the INTFLAG
register to determine which interrupt condition is present.
C
MIN
Vmes Vout
MAX
–()
Δtemperature
Δvoltage
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