Datasheet

supply level, and is specified in Electrical Characteristics. During the start-up time, the COMP output is
not available.
The comparator can be configured to generate interrupts when the output toggles, when the output
changes from '0' to '1' (rising edge), when the output changes from '1' to '0' (falling edge) or at the end of
the comparison. An end-of-comparison interrupt can be used with the single-shot mode to chain further
events in the system, regardless of the state of the comparator outputs. The interrupt mode is set by the
Interrupt Selection bit group in the Comparator Control register (COMPCTRLx.INTSEL). Events are
generated using the comparator output state, regardless of whether the interrupt is enabled or not.
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37. Electrical Characteristics
34.6.2.4.1 Continuous Measurement
Continuous measurement is selected by writing COMPCTRLx.SINGLE to zero. In continuous mode, the
comparator is continuously enabled and performing comparisons. This ensures that the result of the
latest comparison is always available in the Current State bit in the Status A register (STATUSA.STATEx).
After the start-up time has passed, a comparison is done and STATUSA is updated. The Comparator x
Ready bit in the Status B register (STATUSB.READYx) is set, and the appropriate peripheral events and
interrupts are also generated. New comparisons are performed continuously until the
COMPCTRLx.ENABLE bit is written to zero. The start-up time applies only to the first comparison.
In continuous operation, edge detection of the comparator output for interrupts is done by comparing the
current and previous sample. The sampling rate is the CLK_AC_DIG frequency. An example of
continuous measurement is shown in the next figure.
Figure 34-3. Continuous Measurement Example
GCLK_AC
STATUSB.READYx
Sampled
Comparator Output
COMPCTRLx.ENABLE
t
STARTUP
Write ‘1’
2-3 cycles
For low-power operation, comparisons can be performed during sleep modes without a clock. The
comparator is enabled continuously, and changes of the comparator state are detected asynchronously.
When a toggle occurs, the Power Manager will start CLK_AC_DIG to register the appropriate peripheral
events and interrupts. The CLK_AC_DIG clock is then disabled again automatically, unless configured to
wake up the system from sleep.
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37. Electrical Characteristics
34.6.2.4.2 Single-Shot
Single-shot operation is selected by writing COMPCTRLx.SINGLE to '1'. During single-shot operation, the
comparator is normally idle. The user starts a single comparison by writing '1' to the respective Start
Comparison bit in the write-only Control B register (CTRLB.STARTx). The comparator is enabled, and
after the start-up time has passed, a single comparison is done and STATUSA is updated. Appropriate
peripheral events and interrupts are also generated. No new comparisons will be performed.
Writing '1' to CTRLB.STARTx also clears the Comparator x Ready bit in the Status B register
(STATUSB.READYx). STATUSB.READYx is set automatically by hardware when the single comparison
has completed.
SAM D21 Family
AC – Analog Comparators
© 2018 Microchip Technology Inc.
Datasheet Complete
DS40001882D-page 935