SAM7S256_14 Datasheet, PDF (544/775 Pages) ATMEL Corporation – ARM-based Flash MCU

36.5.5 Conversion Triggers
Conversions of the active analog channels are started with a software or a hardware trigger. The software trigger is
provided by writing the Control Register (ADC_CR) with the bit START at 1.
The hardware trigger can be one of the TIOA outputs of the Timer Counter channels, or the external trigger input of
the ADC (ADTRG). The hardware trigger is selected with the field TRGSEL in the Mode Register (ADC_MR). The
selected hardware trigger is enabled with the bit TRGEN in the Mode Register (ADC_MR).
If a hardware trigger is selected, the start of a conversion is triggered after a delay starting at each rising edge of
the selected signal. Due to asynchronism handling, the delay may vary in a range of 2 MCK clock periods to 1 ADC
clock period.
trigger
start
delay
If one of the TIOA outputs is selected, the corresponding Timer Counter channel must be programmed in Wave-
form Mode.
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 enable the analog channels to be enabled or
disabled independently.
If the ADC is used with a PDC, only the transfers of converted data from enabled channels are performed and the
resulting data buffers should be interpreted accordingly.
Warning: Enabling hardware triggers does not disable the software trigger functionality. Thus, if a hardware trigger
is selected, the start of a conversion can be initiated either by the hardware or the software trigger.
36.5.6 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 bit SLEEP in the Mode Register ADC_MR.
The SLEEP mode is automatically managed by a conversion sequencer, which can automatically process the con-
versions of all channels at lowest power consumption.
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 conversion sequencer allows automatic processing with minimum processor intervention and optimized power
consumption. Conversion sequences can be performed periodically using a Timer/Counter output. The periodic
acquisition of several samples can be processed automatically without any intervention of the processor thanks to
the PDC.
Note: The reference voltage pins always remain connected in normal mode as in sleep mode.
SAM7S Series [DATASHEET]
6175M–ATARM–26-Oct-12
544