57.6.9 Comparison Window

The ADC Controller features automatic comparison functions. It compares converted values to a low threshold, a high threshold or both, depending on the value of the ADC_EMR.CMPMODE field. The comparison can be done on all channels or only on the channel specified in the ADC_EMR.CMPSEL field. To compare all channels, ADC_EMR.CMPALL must be set.

If set, ADC_EMR.CMPTYPE can be used to discard all conversion results that do not match the comparison conditions. Once a conversion result matches the comparison conditions, all the subsequent conversion results are stored in ADC_LCDR (even if these results do not meet the comparison conditions). Setting ADC_CR.CMPRST immediately stops the conversion result storage until the next comparison match.

If ADC_EMR.CMPTYPE is cleared, all conversions are stored in ADC_LCDR. Only the conversions that match the comparison conditions trigger the ADC_ISR.COMPE flag.

Moreover, a filtering option can be set by writing the number of consecutive comparison matches needed to raise the flag. This number can be written and read in the ADC_EMR.CMPFILTER field. The filtering option is dedicated to reinforcing the detection of an analog signal overpassing a predefined threshold. The filter is cleared as soon as ADC_ISR is read, so this filtering function must be used with peripheral DMA controller and works only when using Interrupt mode (no polling).

The flag can be read on ADC_ISR.COMPE and can trigger an interrupt.

The high threshold and the low threshold can be read/write in the Compare Window register (ADC_CWR).

Depending on the sign of the conversion, chosen with the ADC_EMR.SIGNMODE field, the high threshold and low threshold values must be signed or unsigned to maintain consistency during the comparison. If the conversion is signed, both thresholds must also be signed; if the conversion is unsigned, both thresholds must be unsigned. If comparison occurs on all channels, the ADC_EMR.SIGNMODE field must be set to ALL_UNSIGNED or ALL_SIGNED and the thresholds must be set accordingly.