STM32 ADC principle

The number of ADC bits determines the accuracy of ADC, which can be 8-bit, 12-bit, 16-bit, etc.

Another very important parameter is the conversion time.

ST M32f103RBT6 has 2 ADC controllers . 128KFlash, 20KRAM

Each ADC controller has multiple channels. For example, ADC1 has 16 external channels. It can be understood that there is a switch connecting each channel.

The sampling interval and sampling time of each channel can be set.

3. ADC channels and IO pin correspondence table

Generally, the negative reference voltage is connected to ground and the positive reference voltage is connected to 3.3V .

The analog input voltage cannot exceed 3.3V, otherwise the input pin may be burned.

ADC Block Diagram

Vref+ is connected to VDDA and Vref- is connected to VSSA.

A maximum of 4 channels are connected to the injection channel and a maximum of 16 channels are connected to the regular channel.

What is a regular channel: Equivalent to a normally running program, up to 16 channels, the regular channel and its conversion order are selected in ADC_SQRx, and the total number of regular group conversions should be written to L[3:0] of the ADC_SQR1 register .

The result of rule channel conversion is saved in the rule channel.

What is an injection channel: Equivalent to an interrupt, with a maximum of 4 injection channels. The injection group and its conversion order are selected in the ADC_JSQR register, and the total number of conversions in the injection group should be written to L[1:0] of the ADC_JSQR register.

The result of the injection channel conversion is saved in the data register of the injection channel.

Regular Channel VS Injection Channel

4. Single Conversion vs Continuous Conversion

After a single conversion is completed, it will not automatically switch to the conversion of another channel. Manual setting is required to start it. Continuous conversion means that another conversion will be automatically started immediately after the ADC conversion is completed.

Scan Mode

An EOC or JEOC interrupt is generated only after the last channel has been converted. Data is usually read via DMA.

5. ADC Interrupt

6. ADC clock configuration

For example: if the system clock is 72M, you need to choose 6-division or 8-division, and 6-division is 12M.

7. ADC_CR1 Register

Here we generally choose independent mode.

8. ADC_CR2 Register

IX. Alignment

Because STM32 is 12-bit AD and the register is 16 bits, you need to select the alignment method.

The software conversion selected in this experiment is that the 19:17 bits are set to 111.

10. ADC_SMPR1 Register

11. ADC_SMPR2 Register

The ADC clock has been set by the RCC_CFGR register.

The ADC_SMPR1 and ADC_SMPR2 registers are used to set the sampling time of channels 0 to 17. The sampling time of each ADC channel can be set independently.

Note: The minimum conversion time should be 1us

The minimum conversion time is 1us.

12. ADC_SQR1, SQR2, SQR3 regular sequence registers

Set the length of the regular channel sequence, which channel the first conversion corresponds to, which channel the second conversion corresponds to, and so on.

13. ADC_JSQR injection series register

14. ADC_DR Regular Channel Data Register

We mainly use the lower 16 bits here.

15. ADC_SR Status Register

16. Commonly used library functions for ADC

example: