Atmel Evaluation Kit AT91SAM9G25-EK AT91SAM9G25-EK Data Sheet
Product codes
AT91SAM9G25-EK
870
SAM9G25 [DATASHEET]
11032C–ATARM–25-Jan-13
Only one start command is necessary to initiate a conversion sequence on all the channels. The ADC hardware logic
automatically performs the conversions on the active channels, then waits for a new request. The Channel Enable
(ADC_CHER) and Channel Disable (ADC_CHDR) Registers permit the analog channels to be enabled or disabled
independently.
automatically performs the conversions on the active channels, then waits for a new request. The Channel Enable
(ADC_CHER) and Channel Disable (ADC_CHDR) Registers permit the analog channels to be enabled or disabled
independently.
If the ADC is used with a DMA , only the transfers of converted data from enabled channels are performed and the
resulting data buffers should be interpreted accordingly.
resulting data buffers should be interpreted accordingly.
40.6.6 Sleep Mode and Conversion Sequencer
The ADC Sleep Mode maximizes power saving by automatically deactivating the ADC when it is not being used for
conversions. Sleep Mode is selected by setting the SLEEP bit in the Mode Register ADC_MR.
conversions. Sleep Mode is selected by setting the SLEEP bit in the Mode Register ADC_MR.
The Sleep mode is automatically managed by a conversion sequencer, which can automatically process the conversions
of all channels at lowest power consumption.
of all channels at lowest power consumption.
This mode can be used when the minimum period of time between 2 successive trigger events is greater than the startup
period of Analog-Digital converter (See the product ADC Characteristics section).
period of Analog-Digital converter (See the product ADC Characteristics section).
When a start conversion request occurs, the ADC is automatically activated. As the analog cell requires a start-up time,
the logic waits during this time and starts the conversion on the enabled channels. When all conversions are complete,
the ADC is deactivated until the next trigger. Triggers occurring during the sequence are not taken into account.
the logic waits during this time and starts the conversion on the enabled channels. When all conversions are complete,
the ADC is deactivated until the next trigger. Triggers occurring during the sequence are not taken into account.
The conversion sequencer allows automatic processing with minimum processor intervention and optimized power
consumption. Conversion sequences can be performed periodically usingthe internal timer (ADC_TRGR register) . The
periodic acquisition of several samples can be processed automatically without any intervention of the processor thanks
to the DMA.
consumption. Conversion sequences can be performed periodically usingthe internal timer (ADC_TRGR register) . The
periodic acquisition of several samples can be processed automatically without any intervention of the processor thanks
to the DMA.
The sequence can be customized by programming the Sequence Channel Registers, ADC_SEQR1 and ADC_SEQR2
and setting to 1 the USEQ bit of the Mode Register (ADC_MR). The user can choose a specific order of channels and
can program up to 12 conversions by sequence. The user is totally free to create a personal sequence, by writing
channel numbers in ADC_SEQR1 and ADC_SEQR2. Not only can channel numbers be written in any sequence,
channel numbers can be repeated several times. Only enabled sequence bitfields are converted, consequently to
program a 15-conversion sequence, the user can simply put a disable in ADC_CHSR[15], thus disabling the 16THCH
field of ADC_SEQR2.
and setting to 1 the USEQ bit of the Mode Register (ADC_MR). The user can choose a specific order of channels and
can program up to 12 conversions by sequence. The user is totally free to create a personal sequence, by writing
channel numbers in ADC_SEQR1 and ADC_SEQR2. Not only can channel numbers be written in any sequence,
channel numbers can be repeated several times. Only enabled sequence bitfields are converted, consequently to
program a 15-conversion sequence, the user can simply put a disable in ADC_CHSR[15], thus disabling the 16THCH
field of ADC_SEQR2.
If all ADC channels (i.e. 12) are used on an application board, there is no restriction of usage of the user sequence. But
as soon as some ADC channels are not enabled for conversion but rather used as pure digital inputs, the respective
indexes of these channels cannot be used in the user sequence fields (ADC_SEQR1, ADC_SEQR2 bitfields).
For example, if channel 4 is disabled (ADC_CSR[4] = 0), ADC_SEQR1, ADC_SEQR2 register bitfields USCH1 up to
USCH12 must not contain the value 4. Thus the length of the user sequence may be limited by this behavior.
as soon as some ADC channels are not enabled for conversion but rather used as pure digital inputs, the respective
indexes of these channels cannot be used in the user sequence fields (ADC_SEQR1, ADC_SEQR2 bitfields).
For example, if channel 4 is disabled (ADC_CSR[4] = 0), ADC_SEQR1, ADC_SEQR2 register bitfields USCH1 up to
USCH12 must not contain the value 4. Thus the length of the user sequence may be limited by this behavior.
As an example, if only 4 channels over 12 (CH0 up to CH3) are selected for ADC conversions, the user sequence length
cannot exceed 4 channels. Each trigger event may launch up to 4 successive conversions of any combination of
channels 0 up to 3 but no more (i.e. in this case the sequence CH0, CH0, CH1, CH1, CH1 is impossible).
cannot exceed 4 channels. Each trigger event may launch up to 4 successive conversions of any combination of
channels 0 up to 3 but no more (i.e. in this case the sequence CH0, CH0, CH1, CH1, CH1 is impossible).
A sequence that repeats several times the same channel requires more enabled channels than channels actually used
for conversion. For example, a sequence like CH0, CH0, CH1, CH1 requires 4 enabled channels (4 free channels on
application boards) whereas only CH0, CH1 are really converted.
for conversion. For example, a sequence like CH0, CH0, CH1, CH1 requires 4 enabled channels (4 free channels on
application boards) whereas only CH0, CH1 are really converted.
Note:
The reference voltage pins always remain connected in normal mode as in sleep mode.
40.6.7 Comparison Window
The ADC Controller features automatic comparison functions. It compares converted values to a low threshold or a high
threshold or both, according to the CMPMODE function chosen in the Extended Mode Register (ADC_EMR). The
comparison can be done on all channels or only on the channel specified in CMPSEL field of ADC_EMR. To compare all
channels the CMP_ALL parameter of ADC_EMR should be set.
threshold or both, according to the CMPMODE function chosen in the Extended Mode Register (ADC_EMR). The
comparison can be done on all channels or only on the channel specified in CMPSEL field of ADC_EMR. To compare all
channels the CMP_ALL parameter of ADC_EMR should be set.
Moreover a filtering option can be set by writing the number of consecutive comparison errors needed to raise the flag.
This number can be written and read in the CMPFILTER field of ADC_EMR.
This number can be written and read in the CMPFILTER field of ADC_EMR.