AT91SAM9G35-CU Datasheet, PDF (878/1224 Pages) ATMEL Corporation – AT91SAM ARM-based Embbedded MPU

41.6 Functional Description
41.6.1 Analog-to-digital Conversion
The ADC uses the ADC Clock to perform conversions. Converting a single analog value to a 10-bit digital data requires
Tracking Clock cycles as defined in the field TRACKTIM of the “ADC Mode Register” on page 897 and Transfer Clock
cycles as defined in the field TRANSFER of the same register. The ADC Clock frequency is selected in the PRESCAL
field of the Mode Register (ADC_MR). The tracking phase starts during the conversion of the previous channel. If the
tracking time is longer than the conversion time, the tracking phase is extended to the end of the previous conversion.
The ADC clock range is between MCK/2, if PRESCAL is 0, and MCK/512, if PRESCAL is set to 255 (0xFF). PRESCAL
must be programmed in order to provide an ADC clock frequency according to the parameters given in the product
Electrical Characteristics section.
Figure 41-2. Sequence of ADC conversions
ADCClock
Trigger event
(Hard or Soft)
ADC_ON
ADC_Start
ADC_eoc
ADC_SEL
LCDR
DRDY
CH0
CH1
CH0
CH2
CH1
Start Up Time ^{Conversion of CH0}
(and tracking of CH0)
Tracking of CH1
Conversion of CH1
Tracking of CH2
41.6.2 Conversion Reference
The conversion is performed on a full range between 0V and the reference voltage pin ADVREF. Analog inputs between
these voltages convert to values based on a linear conversion.
41.6.3 Conversion Resolution
The ADC supports 8-bit or 10-bit resolutions. The 8-bit selection is performed by setting the LOWRES bit in the ADC
Mode Register (ADC_MR). By default, after a reset, the resolution is the highest and the DATA field in the data registers
is fully used. By setting the LOWRES bit, the ADC switches to the lowest resolution and the conversion results can be
read in the lowest significant bits of the data registers. The two highest bits of the DATA field in the corresponding
ADC_CDR register and of the LDATA field in the ADC_LCDR register read 0.
SAM9G35 [DATASHEET]
11053D–ATARM–11-Feb-13
878