ADS1120: Interfacing with STM32

Tool/software:

I am using the ADS1120 to measure RTD (Resistance Temperature Detector) values. I am utilizing AIN1 and AIN2 as the input channels and configuring IDAC1 and IDAC2 for excitation current at 1000 μA (1 mA). Additionally, I need the data rate to be set to 600 SPS (Samples Per Second).

I have already configured and verified the SPI communication to read and write registers, but the ADC readings I get are unstable and incorrect, which I believe might be due to improper configuration of the ADS1120 registers.

Here are the key requirements:

1. AIN1 and AIN2 should be configured as differential inputs.
2. IDAC1 and IDAC2 should output 1000 μA excitation current to the RTD sensor.
3. The data rate should be set to 600 SPS.
4. Ensure proper configuration of registers for stable operation.

Below is my code snippet for configuring the ADS1120 and reading the ADC values. I suspect an issue in register configuration, and I would appreciate help with debugging this.

#include "stm32f4xx_hal.h" // For STM32 environment
#include <stdint.h>

#define ADS1120_CMD_WREG 0x40 // Write to register command
#define ADS1120_CMD_RREG 0x20 // Read register command
#define ADS1120_CMD_START 0x08 // Start a new conversion
#define ADS1120_CMD_RESET 0x06 // Reset command

#define ADS1120_CS_LOW() HAL_GPIO_WritePin(GPIOA, GPIO_PIN_4, GPIO_PIN_RESET)
#define ADS1120_CS_HIGH() HAL_GPIO_WritePin(GPIOA, GPIO_PIN_4, GPIO_PIN_SET)

// SPI handle (configured earlier)
extern SPI_HandleTypeDef hspi3;

// ADS1120 Register Addresses
#define CONFIG_REG_0 0x00
#define CONFIG_REG_1 0x01
#define CONFIG_REG_2 0x02
#define CONFIG_REG_3 0x03

// Function Prototypes
void ADS1120_Reset(void);
void ADS1120_Config(void);
uint16_t ADS1120_ReadData(void);
void ADS1120_WriteRegister(uint8_t reg, uint8_t value);
uint8_t ADS1120_ReadRegister(uint8_t reg);

// ADS1120 Reset Function
void ADS1120_Reset(void) {
ADS1120_CS_LOW();
HAL_SPI_Transmit(&hspi3, (uint8_t[]){ADS1120_CMD_RESET}, 1, HAL_MAX_DELAY);
HAL_Delay(2); // Wait for ADS1120 reset completion
ADS1120_CS_HIGH();
}

// ADS1120 Configuration Function
void ADS1120_Config(void) {
// Configuration Register 0 (MUX, PGA, and Data Rate)
// MUX: AIN1-AIN2 (differential), PGA = 1, Data Rate = 600 SPS
uint8_t config0 = 0b00110010; // MUX[3:0]=0011, PGA=1x, DR=600 SPS

// Configuration Register 1 (Mode, Conversion Mode, and Temperature Sensor)
// Mode = Normal, Conversion Mode = Continuous, IDAC enabled
uint8_t config1 = 0b00000010; // MODE=Normal, CM=Continuous, TS=off, IDAC=Enabled

// Configuration Register 2 (IDAC Current)
// IDAC1 and IDAC2 set to 1000 μA
uint8_t config2 = 0b00001100; // IDAC1 and IDAC2 = 1000 μA

// Configuration Register 3 (IDAC Routing)
// Route IDAC1 to AIN1 and IDAC2 to AIN2
uint8_t config3 = 0b00011011; // I1DIR=AIN1, I2DIR=AIN2

// Write to ADS1120 registers
ADS1120_WriteRegister(CONFIG_REG_0, config0);
ADS1120_WriteRegister(CONFIG_REG_1, config1);
ADS1120_WriteRegister(CONFIG_REG_2, config2);
ADS1120_WriteRegister(CONFIG_REG_3, config3);
}

// Function to Write a Register
void ADS1120_WriteRegister(uint8_t reg, uint8_t value) {
uint8_t command = ADS1120_CMD_WREG | (reg & 0x03); // Write command with register address
ADS1120_CS_LOW();
HAL_SPI_Transmit(&hspi3, &command, 1, HAL_MAX_DELAY);
HAL_SPI_Transmit(&hspi3, &value, 1, HAL_MAX_DELAY);
ADS1120_CS_HIGH();
}

// Function to Read Data from ADC
uint16_t ADS1120_ReadData(void) {
uint8_t command = ADS1120_CMD_START; // Send START command
uint8_t data[2] = {0};
uint16_t adcResult = 0;

ADS1120_CS_LOW();
HAL_SPI_Transmit(&hspi3, &command, 1, HAL_MAX_DELAY);
HAL_SPI_Receive(&hspi3, data, 2, HAL_MAX_DELAY);
ADS1120_CS_HIGH();

// Combine MSB and LSB
adcResult = ((uint16_t)data[0] << 8) | data[1];
return adcResult;
}

int main(void) {
HAL_Init(); // Initialize HAL
// Configure peripherals, clocks, SPI, and GPIO here

ADS1120_Reset(); // Reset ADS1120
ADS1120_Config(); // Configure ADS1120

while (1) {
uint16_t adcValue = ADS1120_ReadData();
printf("ADC Value: %u\n", adcValue);
HAL_Delay(100); // Adjust delay as needed
}
}

static void MX_SPI3_Init(void)
{

/* USER CODE BEGIN SPI3_Init 0 */

/* USER CODE END SPI3_Init 0 */

/* USER CODE BEGIN SPI3_Init 1 */

/* USER CODE END SPI3_Init 1 */
/* SPI3 parameter configuration*/
hspi3.Instance = SPI3;
hspi3.Init.Mode = SPI_MODE_MASTER;
hspi3.Init.Direction = SPI_DIRECTION_2LINES;
hspi3.Init.DataSize = SPI_DATASIZE_16BIT;
hspi3.Init.CLKPolarity = SPI_POLARITY_LOW;
hspi3.Init.CLKPhase = SPI_PHASE_1EDGE;
hspi3.Init.NSS = SPI_NSS_SOFT;
hspi3.Init.BaudRatePrescaler = SPI_BAUDRATEPRESCALER_8;
hspi3.Init.FirstBit = SPI_FIRSTBIT_MSB;
hspi3.Init.TIMode = SPI_TIMODE_DISABLE;
hspi3.Init.CRCCalculation = SPI_CRCCALCULATION_DISABLE;
hspi3.Init.CRCPolynomial = 10;
if (HAL_SPI_Init(&hspi3) != HAL_OK)
{
Error_Handler();
}
/* USER CODE BEGIN SPI3_Init 2 */

/* USER CODE END SPI3_Init 2 */

}