Datasheet

907

SAM9G25 [DATASHEET]

11032D–ATARM–10-Mar-2014

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.

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.

The flag can be read on the COMPE bit of the Interrupt Status Register (ADC_ISR) and can trigger an interrupt.

The High Threshold and the Low Threshold can be read/write in the Comparison Window Register (ADC_CWR).

If the comparison window is to be used with LOWRES bit in ADC_MR set to 1, the thresholds do not need to be adjusted

as adjustment will be done internally. Whether or not the LOWRES bit is set, thresholds must always be configured in

consideration of the maximum ADC resolution.

40.6.8 ADC Timings

Each ADC has its own minimal Startup Time that is programmed through the field STARTUP in the Mode Register,

ADC_MR.

A minimal Tracking Time is necessary for the ADC to guarantee the best converted final value between two channel

selections. This time has to be programmed through the TRACKTIM bit field in the Mode Register, ADC_MR.

Warning: No input buffer amplifier to isolate the source is included in the ADC. This must be taken into consideration to

program a precise value in the TRACKTIM field. See the product ADC Characteristics section.

40.6.9 Buffer Structure

The DMA read channel is triggered each time a new data is stored in ADC_LCDR register. The same structure of data is

repeatedly stored in ADC_LCDR register each time a trigger event occurs. Depending on user mode of operation

(ADC_MR, ADC_CHSR, ADC_SEQR1, ADC_SEQR2) the structure differs. Each data transferred to DMA buffer, carried

on a half-word (16-bit), consists of last converted data right aligned and when TAG is set in ADC_EMR register, the 4

most significant bits are carrying the channel number thus allowing an easier post-processing in the DMA buffer or better

checking the DMA buffer integrity.

40.6.10 Write Protected Registers

To prevent any single software error that may corrupt ADC behavior, certain address spaces can be write-protected by

setting the WPEN bit in the “ADC Write Protect Mode Register” (ADC_WPMR).

If a write access to the protected registers is detected, then the WPVS flag in the ADC Write Protect Status Register

(ADC_WPSR) is set and the field WPVSRC indicates in which register the write access has been attempted.

The WPVS flag is automatically reset by reading the ADC Write Protect Status Register (ADC_WPSR).