ADC Multi-Channel has a problem.

Posted on January 27, 2014 at 06:13

Hello,

I have many questions about ADC Multi-Channel to ask and thank you for your helping. I used STM32F417ZGT6.

1. I used ADC to read voltage in 2 channel with below setting.

01./* Enable ADCx, DMA and GPIO clocks ****************************************/

02.    RCC_AHB1PeriphClockCmd ( RCC_AHB1Periph_DMA2, ENABLE );

03.    RCC_AHB1PeriphClockCmd ( SS_AI_RJA7_GPIO_CLK | SS_AI_RJB7_GPIO_CLK, ENABLE );

04.    RCC_APB2PeriphClockCmd ( SS_AI_ADC_CLK, ENABLE );

05. 

06.    /* Configure ADC3 Channel7 pin as analog input ******************************/

07.    GPIO_InitStructure.GPIO_Mode = GPIO_Mode_AN;

08.    GPIO_InitStructure.GPIO_PuPd = GPIO_PuPd_NOPULL;

09. 

10.    GPIO_InitStructure.GPIO_Pin = SS_AI_RJA7_PIN;

11.    GPIO_Init ( SS_AI_RJA7_GPIO_PORT, &GPIO_InitStructure );

12. 

13.    GPIO_InitStructure.GPIO_Pin = SS_AI_RJB7_PIN;

14.    GPIO_Init ( SS_AI_RJB7_GPIO_PORT, &GPIO_InitStructure );

15. 

16.    DMA_DeInit (DMA2_Stream0);

17. 

18.    /* DMA2 Stream0 channel2 configuration **************************************/

19.    DMA_InitStructure.DMA_Channel               = DMA_Channel_2;

20.    DMA_InitStructure.DMA_PeripheralBaseAddr    = (uint32_t) &ADC3->DR;

21.    DMA_InitStructure.DMA_Memory0BaseAddr       = (uint32_t) &ADCValue[0];

22.    DMA_InitStructure.DMA_DIR                   = DMA_DIR_PeripheralToMemory;

23.    DMA_InitStructure.DMA_BufferSize            = 2;

24.    DMA_InitStructure.DMA_PeripheralInc         = DMA_PeripheralInc_Disable;

25.    DMA_InitStructure.DMA_MemoryInc             = DMA_MemoryInc_Enable;

26.    DMA_InitStructure.DMA_PeripheralDataSize    = DMA_PeripheralDataSize_HalfWord;

27.    DMA_InitStructure.DMA_MemoryDataSize        = DMA_MemoryDataSize_HalfWord;

28.    DMA_InitStructure.DMA_Mode                  = DMA_Mode_Circular;

29.    DMA_InitStructure.DMA_Priority              = DMA_Priority_High;

30.    DMA_InitStructure.DMA_FIFOMode              = DMA_FIFOMode_Disable;

31.    DMA_InitStructure.DMA_FIFOThreshold         = DMA_FIFOThreshold_HalfFull;

32.    DMA_InitStructure.DMA_MemoryBurst           = DMA_MemoryBurst_Single;

33.    DMA_InitStructure.DMA_PeripheralBurst       = DMA_PeripheralBurst_Single;

34. 

35.    DMA_Init ( DMA2_Stream0, &DMA_InitStructure );

36.    DMA_Cmd ( DMA2_Stream0, ENABLE );

37. 

38.    /* ADC Common Init **********************************************************/

39.    ADC_CommonInitStructure.ADC_Mode = ADC_Mode_Independent;

40.    ADC_CommonInitStructure.ADC_Prescaler = ADC_Prescaler_Div2;

41.    ADC_CommonInitStructure.ADC_DMAAccessMode = ADC_DMAAccessMode_Disabled;

42.    ADC_CommonInitStructure.ADC_TwoSamplingDelay = ADC_TwoSamplingDelay_5Cycles;

43.    ADC_CommonInit ( &ADC_CommonInitStructure );

44. 

45.    /* ADC3 Init ****************************************************************/

46.    ADC_InitStructure.ADC_Resolution = ADC_Resolution_12b;

47.    ADC_InitStructure.ADC_ScanConvMode = ENABLE;

48.    ADC_InitStructure.ADC_ContinuousConvMode = DISABLE;

49.    ADC_InitStructure.ADC_ExternalTrigConvEdge = ADC_ExternalTrigConvEdge_None;

50.    ADC_InitStructure.ADC_ExternalTrigConv = ADC_ExternalTrigConv_T1_CC1;

51.    ADC_InitStructure.ADC_DataAlign = ADC_DataAlign_Right;

52.    ADC_InitStructure.ADC_NbrOfConversion = 2;

53.    ADC_Init ( SS_AI_ADC, &ADC_InitStructure );

54. 

55.    /* ADC3 regular channel7 configuration **************************************/

56.    ADC_RegularChannelConfig ( SS_AI_ADC, SS_AI_RJA7_ADC_CH, 1, ADC_SampleTime_15Cycles );

57.    ADC_RegularChannelConfig ( SS_AI_ADC, SS_AI_RJB7_ADC_CH, 2, ADC_SampleTime_15Cycles );

58. 

59.    /* Enable DMA request after last transfer (Single-ADC mode) */

60.    ADC_DMARequestAfterLastTransferCmd ( SS_AI_ADC, ENABLE );

61.    /* Enable ADC3 DMA */

62.    ADC_DMACmd ( SS_AI_ADC, ENABLE );

63.    /* Enable ADC3 */

64.    ADC_Cmd ( SS_AI_ADC, ENABLE );

65. 

66.    ADC_SoftwareStartConv(SS_AI_ADC);

But I have a problem when I put voltage to adc with this

1. I measure voltage before I plug it to MCU, about 1.185V 

2. Plug it and measure again, about 1.181V 

3. When I plug another input on another channel with 2.501V. The old one will be 1.200V. 

This value is used multimeter for measurement. And I try to read adc value, 

they have same value about 2.501V and 1.200V But it is not stable, it is about 2.492-2.508 when I put 2.501V. 

However, The actual value is about 1.185V and 2.501 V. 

Then I changed sampling rate from ADC_SampleTime_15Cycles to ADC_SampleTime_480Cycles. The voltage don't changed when I plug it.

But the value is not stable. When I used only one channel, I used ADC_SampleTime_15Cycles

and the value is enough accurate. I put 2.501 and can read 2.498-2.502 that's ok. 

2. Can I turn off ADC and come back to read normal GPIO? And Can they come back again to read an ADC? How can I do it? And it is very important to not loss an accuracy on ADC.

Thank you very much to helping.

#stm32f4 #adc_multi-channel