Configuring ADC registers for conversion

AN3023

10/23

Doc ID 16113 Rev 1

3.1.3

Channel selection

There are up to 16 input channels in ADC and up to 12 input channels in ADC2 (the

maximum number of channels per ADC peripheral depends on the MCU package size).

External input channels can be selected by bits CH[3:0] in the ADC_CSR register. If the

channel is changed during an ongoing conversion, the current conversion is reset and a new

start pulse is sent to ADC.

3.1.4

Conversion on external trigger

Conversion can also be started by an external trigger event after ADC power ON.

external trigger and the bits EXTSEL[1:0] select the trigger source as either the timer or the

external trigger pin.

The different software sequences (shown below) to select the trigger source and enable the

external trigger depend on the ADC state (powered-ON or powered-OFF).

Case 1: ADC is in powered-ON state

ADC_CR2 = value1; Select the source (EXTSEL[1:0] bits)

ADC_CR2 |= 0x40; Enable external trigger (EXTTRIG bit)

Case 2: ADC is in powered-OFF state

When the ADC is in powered-OFF state, the user is free to choose between the above

software sequence, that is, for ADC powered-ON state or the sequence below:

ADC_CR2 = value; Select the source and enable the external trigger

3.1.5

Conversion modes

Single conversion mode

In single conversion mode, the ADC performs one conversion on the channel selected by

bits CH[3:0] in the ADC_CSR register. At the end of conversion, the EOC bit is set and the

result can be read from the registers ADC_DRH and ADC_DRL. The interrupt is generated

if the EOC interrupt is enabled in the ADC_CSR register.

Example 1

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Channel = AIN1

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Single conversion mode, left alignment mode

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Starting ADC by software

b.

Refer to the datasheet for the details on the trigger source available.