DocID024597 Rev 3 535/1693
RM0351 Analog-to-digital converters (ADC)
540
Bits 21:18 PRESC[3:0]: ADC prescaler
These bits are set and cleared by software to select the frequency of the clock to the ADC.
The clock is common for all the ADCs.
0000: input ADC clock not divided
0001: input ADC clock divided by 2
0010: input ADC clock divided by 4
0011: input ADC clock divided by 6
0100: input ADC clock divided by 8
0101: input ADC clock divided by 10
0110: input ADC clock divided by 12
0111: input ADC clock divided by 16
1000: input ADC clock divided by 32
1001: input ADC clock divided by 64
1010: input ADC clock divided by 128
1011: input ADC clock divided by 256
other: reserved
Note: Software is allowed to write these bits only when the ADC is disabled (ADCAL=0,
JADSTART=0, ADSTART=0, ADSTP=0, ADDIS=0 and ADEN=0). The ADC prescaler
value is applied only when CKMODE[1:0] = 0b00.
Bits 17:16 CKMODE[1:0]: ADC clock mode
These bits are set and cleared by software to define the ADC clock scheme (which is
common to both master and slave ADCs):
00: CK_ADCx (x=123) (Asynchronous clock mode), generated at product level (refer to
Section 6: Reset and clock control (RCC))
01: HCLK/1 (Synchronous clock mode). This configuration must be enabled only if the AHB
clock prescaler is set to 1 (HPRE[3:0] = 0xxx in RCC_CFGR register) and if the system clock
has a 50% duty cycle.
10: HCLK/2 (Synchronous clock mode)
11: HCLK/4 (Synchronous clock mode)
In all synchronous clock modes, there is no jitter in the delay from a timer trigger to the start
of a conversion.
Note: Software is allowed to write these bits only when the ADCs are disabled (ADCAL=0,
JADSTART=0, ADSTART=0, ADSTP=0, ADDIS=0 and ADEN=0).
Bits 15:14 MDMA[1:0]: Direct memory access mode for dual ADC mode
This bit-field is set and cleared by software. Refer to the DMA controller section for more
details.
00: MDMA mode disabled
01: reserved
10: MDMA mode enabled for 12 and 10-bit resolution
11: MDMA mode enabled for 8 and 6-bit resolution
Note: Software is allowed to write these bits only when ADSTART=0 (which ensures that no
regular conversion is ongoing).
Bit 13 DMACFG: DMA configuration (for dual ADC mode)
This bit is set and cleared by software to select between two DMA modes of operation and is
effective only when DMAEN=1.
0: DMA One Shot Mode selected
1: DMA Circular Mode selected
For more details, refer to Section : Managing conversions using the DMA
Note: Software is allowed to write these bits only when ADSTART=0 (which ensures that no
regular conversion is ongoing).
Bit 12 Reserved, must be kept at reset value.
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