STM32 SPI Master Receiving

[AE104]

Hello,

On my custom design board, I use external 12 bit ADC (ADS7886) and STM32F767VI. I try to get digitized ADC values with SPI interface. I set the SPI as Receive only master than prescaler as 8; baudrate as 13.5 Mbits/s; polarity as 1; phase as 1; data size as 16 bits; MSB.

My C code in Keil is

uint16_t ADC_Buf;

if(Rx_flag)

{

HAL_GPIO_WritePin(ADC_CS_GPIO_Port, ADC_CS_Pin, GPIO_PIN_RESET);

HAL_SPI_Receive(&hspi4, (uint8_t*)&ADC_Buf,2,100);

volt = (float)(ADC_Buf * 5 / pow(2,12)); // 

HAL_GPIO_WritePin(ADC_CS_GPIO_Port, ADC_CS_Pin, GPIO_PIN_SET);

Rx_flag = 0;

}

I enabled SPI global interrupt. Then I set a timer. Timer frequency is at least 10 times bigger frequency than the input signal frequency. Every each interrupt of the timer, a flag is active then transmission happen. But I didn't plot in STM Studio and observe in debugger mode successfully yet. For example, now my input signal frequency is 1.96kHZ and I set the timer as 20kHz.

Do you have any idea to solve this problem?

Thank you,

[waclawek.jan]

Maybe you want to take one step at a time.

Starting with basic blinky, then with PWM, determining proper timing, etc.

JW

[S.Ma]

If in your mind spi master means you are in control of the sck clock generation, then only spi full duplex bi directional 4 wire shall meet expectations.

[AE104]

Actually, the number of clk (yellow) is around 48 counts. It should be 16 numbers of clk during data transmission based on the datasheet. So why I get 48 counts and how can i get 16 of them?

[waclawek.jan]

Just don't use the Receive-only mode. It immediately starts to generate clocks as soon as you enable it, and it won't stop until you disable it.

Use normal duplex mode as KIC/HD said above; you don't need to bring out MOSI to a pin.

JW

[AE104]

I modified SPI mode as full duplex master. Then I make it pull down of MOSI pin. I correctly read a step signal such as 2.3V fed signal to the ADC. But when I feed biphasic signal. I can only read maximum value of the signal. Then I modified my code a little bit such as

uint8_t ADC_Buf[2]; 

float testdata_in[16];

uint8_t i=0;

uint16_t ADC_Buf_Val = 0;

uint16_t Sample;

float volt = 0;

void ADC_Conversion_of_Voltage_Transients()

{

HAL_GPIO_WritePin(ADC_CS_GPIO_Port, ADC_CS_Pin, GPIO_PIN_RESET);

HAL_SPI_Receive(&hspi4,ADC_Buf,2,100);

HAL_GPIO_WritePin(ADC_CS_GPIO_Port, ADC_CS_Pin, GPIO_PIN_SET);

Sample = (((uint16_t) ADC_Buf[1]) << 8 | ADC_Buf[0]);

//Sample = 0x0 << 12 | ADC_Buf;

volt = (float)(Sample * (5.0 / 4096.0)); // 

testdata_in[i++]=volt;

i %= 16;

}

/* SPI4 init function */

static void MX_SPI4_Init(void)

{

 /* SPI4 parameter configuration*/

 hspi4.Instance = SPI4;

 hspi4.Init.Mode = SPI_MODE_MASTER;

 hspi4.Init.Direction = SPI_DIRECTION_2LINES;

 hspi4.Init.DataSize = SPI_DATASIZE_16BIT;

 hspi4.Init.CLKPolarity = SPI_POLARITY_LOW;

 hspi4.Init.CLKPhase = SPI_PHASE_2EDGE;

 hspi4.Init.NSS = SPI_NSS_SOFT;

 hspi4.Init.BaudRatePrescaler = SPI_BAUDRATEPRESCALER_16;

 hspi4.Init.FirstBit = SPI_FIRSTBIT_MSB;

 hspi4.Init.TIMode = SPI_TIMODE_DISABLE;

 hspi4.Init.CRCCalculation = SPI_CRCCALCULATION_DISABLE;

 hspi4.Init.CRCPolynomial = 7;

 hspi4.Init.CRCLength = SPI_CRC_LENGTH_DATASIZE;

 hspi4.Init.NSSPMode = SPI_NSS_PULSE_DISABLE;

 if (HAL_SPI_Init(&hspi4) != HAL_OK)

 {

  _Error_Handler(__FILE__, __LINE__);

 }

}