18-bit SPI

Chuev.Vladimir · ‎2017-09-25

Posted on September 25, 2017 at 15:27

I'm trying to use two AD7690 (18-bit ADC)

http://www.analog.com/media/en/technical-documentation/data-sheets/AD7690.pdf

(page 20)

But when I accept the data, I get a mistake HAL_ERROR

However, I'm getting some data there

HAL_GPIO_WritePin(GPIOA, ADC_CVN_Pin, GPIO_PIN_SET);

HAL_Delay(10);

HAL_SPI_Receive(&spi1, (uint8*)data, 8, 1000);

HAL_GPIO_WritePin(GPIOA, ADC_CVN_Pin, GPIO_PIN_RESET);

spi1.Instance = SPI1;

spi1.Init.Mode = SPI_MODE_MASTER;

spi1.Init.Direction = SPI_DIRECTION_2LINES_RXONLY;

spi1.Init.DataSize = SPI_DATASIZE_8BIT;

spi1.Init.CLKPolarity = SPI_POLARITY_LOW;

spi1.Init.CLKPhase = SPI_PHASE_1EDGE;

spi1.Init.NSS = SPI_NSS_SOFT;

spi1.Init.BaudRatePrescaler = SPI_BAUDRATEPRESCALER_256;

spi1.Init.FirstBit = SPI_FIRSTBIT_MSB;

spi1.Init.TIMode = SPI_TIMODE_DISABLE;

spi1.Init.CRCCalculation = SPI_CRCCALCULATION_DISABLE;

spi1.Init.CRCPolynomial = 10;

How do I solve this problem?

#stm32 #adc #ad7690 #spi #hal

waclawek.jan · ‎2017-09-25

Posted on September 25, 2017 at 22:41

Can you observe the SPI pins using oscilloscope or logic analyzer?

JW

Chuev.Vladimir · ‎2017-09-26

Posted on September 26, 2017 at 09:33

That's what I see on oscilloscope

waclawek.jan · ‎2017-09-26

Posted on September 26, 2017 at 09:40

I don't use Cube but the usage of Rx-only mode may be tricky, as it churns out clocks and may easily lead to overflow if not handled rapidly enough. Use normal duplex mode - you don't need to set the MOSI pin in GPIO at all.

JW

John Craven · ‎2017-09-26

Posted on September 26, 2017 at 16:05

Your scope trace doesn't match your code. your doing 8bit spi and askingfor 8bytes, i would have expect to see64clock cycles. Assuming your doing '3wire no busy mode' on your ADC, you only need 18 clk. So use 8bit x 3 (or maybe 7bit x 3).

I looked at the datasheet, your CONVERT seems wrong. Set Convert high, wait for DATA to go low, then read out data.

int main(void)
{
 /* USER CODE BEGIN 1 */
 /* USER CODE END 1 */
 /* MCU Configuration----------------------------------------------------------*/
 /* Reset of all peripherals, Initializes the Flash interface and the Systick. */
 HAL_Init();
 /* USER CODE BEGIN Init */
 /* USER CODE END Init */
 /* Configure the system clock */
 SystemClock_Config();
 /* USER CODE BEGIN SysInit */
 /* USER CODE END SysInit */
 /* Initialize all configured peripherals */
 MX_GPIO_Init();
 MX_SPI1_Init();
 /* USER CODE BEGIN 2 */
 
 uint8_t buffer[3];
 
 //start first conversion
 HAL_GPIO_WritePin(CONVERT_GPIO_Port,CONVERT_Pin, GPIO_PIN_SET);
 /* USER CODE END 2 */
 /* Infinite loop */
 /* USER CODE BEGIN WHILE */
 while (1)
 {
 /* USER CODE END WHILE */
 /* USER CODE BEGIN 3 */
 //wait for end of conversion
 while (HAL_GPIO_ReadPin(MISO_GPIO_Port, MISO_Pin) == GPIO_PIN_SET);
 //set convert low for readout
 HAL_GPIO_WritePin(CONVERT_GPIO_Port,CONVERT_Pin, GPIO_PIN_RESET);
 //Do SPI Receive
 HAL_SPI_Receive(&hspi1, (uint8_t*)buffer, 3, 1000);
 
 uint32_t data = buffer[0] << 10 + buffer[1] << 2 + buffer[2] >> 6; //19bits
 
 //restart conversion
 HAL_GPIO_WritePin(CONVERT_GPIO_Port,CONVERT_Pin, GPIO_PIN_SET);
 
 //Do other stuff while converting
 HAL_Del(100);
 }
 /* USER CODE END 3 */
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data will have the 18bits that are clocked out.

data packing is based on 8bit setup.

void MX_SPI1_Init(void)
{
 hspi1.Instance = SPI1;
 hspi1.Init.Mode = SPI_MODE_MASTER;
 hspi1.Init.Direction = SPI_DIRECTION_2LINES_RXONLY;
 hspi1.Init.DataSize = SPI_DATASIZE_8BIT;
 hspi1.Init.CLKPolarity = SPI_POLARITY_LOW;
 hspi1.Init.CLKPhase = SPI_PHASE_1EDGE;
 hspi1.Init.NSS = SPI_NSS_SOFT;
 hspi1.Init.BaudRatePrescaler = SPI_BAUDRATEPRESCALER_256;
 hspi1.Init.FirstBit = SPI_FIRSTBIT_MSB;
 hspi1.Init.TIMode = SPI_TIMODE_DISABLE;
 hspi1.Init.CRCCalculation = SPI_CRCCALCULATION_DISABLE;
 hspi1.Init.CRCPolynomial = 7;
 hspi1.Init.CRCLength = SPI_CRC_LENGTH_DATASIZE;
 hspi1.Init.NSSPMode = SPI_NSS_PULSE_ENABLE;
 if (HAL_SPI_Init(&hspi1) != HAL_OK)
 {
 _Error_Handler(__FILE__, __LINE__);
 }
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you could use 7bit frames to minimize the readout time.

hspi1.Init.DataSize = SPI_DATASIZE_7BIT;�?

then data would unpack something like;

uint32_t data = buffer[0] << 12 + buffer[1] << 4 + buffer[2] >> 3;