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Figure 45-2. ADC Prescaler
GCLK_ADCx 9-BIT PRESCALER
CTRLA.PRESCALER[2:0]
DIV256
DIV128
DIV64
DIV32
DIV16
DIV8
DIV4
DIV2
CLK_ADCx
Note:  The minimum prescaling factor is DIV2.
45.6.2.5 Reference Configuration
The ADC has various sources for its reference voltage V
REF
. The Reference Voltage Selection bit field in
the Reference Control register (REFCTRL.REFSEL) determines which reference is selected. By default,
the internal voltage reference VREF is selected. Based on customer application requirements, the
external or internal reference can be selected. Refer to REFCTRL.REFSEL for further details on available
selections.
Related Links
45.8.6 REFCTRL
45.6.2.6 ADC Resolution
The ADC supports 8-bit, 10-bit or 12-bit resolution. Resolution can be changed by writing the Resolution
bit group in the Control B register (CTRLB.RESSEL). By default, the ADC resolution is set to 12 bits. The
resolution affects the propagation delay, see also 45.6.2.8 Conversion Timing and Sampling Rate.
45.6.2.7 Differential and Single-Ended Conversions
The ADC has two conversion options: differential and single-ended.
If the positive input is always positive, the single-ended conversion should be used in order to have full
12-bit resolution in the conversion.
If the positive input level may go below the negative input, the differential mode should be used in order to
get correct results.
The differential mode is enabled by writing a '1' to the DIFFMODE bit in the input control register
(INPUTCTRL.DIFFMODE). Both conversion types could be run in single mode or in free-running mode.
When the free-running mode is selected, an ADC input will continuously sample the input and performs a
new conversion. The INTFLAG.RESRDY bit will be set at the end of each conversion.
45.6.2.8 Conversion Timing and Sampling Rate
The following figure shows the ADC timing for one single conversion. A conversion starts after the
software or event start are synchronized with the GCLK_ADCx clock. The input channel is sampled in the
first half CLK_ADCx period.
SAM D5x/E5x Family Data Sheet
ADC – Analog-to-Digital Converter
© 2019 Microchip Technology Inc.
Datasheet
DS60001507E-page 1590