STM32F103C8T6 Blue Pill Not Detected After Flashing MAX31855 SPI Sample Code

[asking]

Hello STM32 Community,

I am working with an STM32F103C8T6 ("Blue Pill") Original Chip and interfacing it with a MAX31855 thermocouple amplifier over SPI1. I used a sample program generated by ChatGPT, which initializes SPI1 and manually controls the CS pin using MOSI (PA7).

Programmer Used : Original STLINK-V3SET

Hello STM32 Community,

I am working with an STM32F103C8T6 ("Blue Pill") and interfacing it with a MAX31855 thermocouple amplifier over SPI1. I used a sample program generated by ChatGPT, which initializes SPI1 and manually controls the CS pin using MOSI (PA7).

Problem Statement:

The program works only on the first flash when I enter debug mode. As soon as i click on Play Button the board stops getting detected via ST-Link/V2 and cannot be reflashed anymore. I have tried with 2-3 different boards, but all of them stopped responding in the same manner.

What I Have Tried:

1. Checked Hardware Connections:

   • MAX31855 Connections:
     • SCK → PA5
     • DO → PA6 (MISO)
     • CS → PA7 (MOSI, manually controlled)
   • MAX31855 is powered at 3.3V
   • SPI configured in Mode 1 (CPOL = 1, CPHA = 1)

2. Tried Different Debuggers:

   • Used both ST-Link V3/V2 (clone and original) → No detection after first flash.
   • Tried USB-TTL for Serial Debugging → No response from board.

3. Checked Boot Modes:

   • Tried Boot0 = 1 (DFU Mode) → No detection in STM32CubeProgrammer.
   • Tried Boot0 = 0 (Normal Mode) → Board still unresponsive.

4. Tried Different Boards:

   • All boards worked fine initially but stopped working after flashing this particular MAX31855 program.

5. Power Supply Checks:

   • Measured 3.3V Rail → Voltage remains stable.
   • Checked VDD and NRST Pins → No noticeable issues.

/* USER CODE BEGIN Header */
/**
  ******************************************************************************
  * @file           : main.c
  * @brief          : Main program body
  ******************************************************************************
  * @attention
  *
  * Copyright (c) 2025 STMicroelectronics.
  * All rights reserved.
  *
  * This software is licensed under terms that can be found in the LICENSE file
  * in the root directory of this software component.
  * If no LICENSE file comes with this software, it is provided AS-IS.
  *
  ******************************************************************************
  */
/* USER CODE END Header */
/* Includes ------------------------------------------------------------------*/
#include "main.h"

/* Private includes ----------------------------------------------------------*/
/* USER CODE BEGIN Includes */
#define CS_PIN     GPIO_PIN_7  // PA7 (MOSI used as CS)
#define CS_PORT    GPIOA
/* USER CODE END Includes */

/* Private typedef -----------------------------------------------------------*/
/* USER CODE BEGIN PTD */

/* USER CODE END PTD */

/* Private define ------------------------------------------------------------*/
/* USER CODE BEGIN PD */
float temperature = 0.0;
/* USER CODE END PD */

/* Private macro -------------------------------------------------------------*/
/* USER CODE BEGIN PM */

/* USER CODE END PM */

/* Private variables ---------------------------------------------------------*/
SPI_HandleTypeDef hspi1;

/* USER CODE BEGIN PV */
uint32_t MAX31855_Read(void) {
    uint8_t data[4] = {0, 0, 0, 0};
    uint32_t rawData = 0;

    // Pull CS low (start communication)
    HAL_GPIO_WritePin(CS_PORT, CS_PIN, GPIO_PIN_RESET);
    HAL_Delay(1);  // Short delay

    // Read 32-bit data
    HAL_SPI_Receive(&hspi1, data, 4, 100);

    // Pull CS high (end communication)
    HAL_GPIO_WritePin(CS_PORT, CS_PIN, GPIO_PIN_SET);

    // Combine bytes into a single 32-bit variable
    rawData = ((uint32_t)data[0] << 24) |
              ((uint32_t)data[1] << 16) |
              ((uint32_t)data[2] <<   |
              ((uint32_t)data[3]);

    return rawData;
}

/**
 * @brief Get temperature from MAX31855.
 */
float MAX31855_GetTemperature(void) {
    uint32_t rawData = MAX31855_Read();

    // Check for fault
    if (rawData & 0x00010000) {
       // printf("Fault detected!\n");
        return -999.0;  // Error value
    }

    // Extract temperature (bits 31-18)
    int16_t tempData = (rawData >> 18) & 0x3FFF;

    // Convert to float (each bit = 0.25°C)
    if (tempData & 0x2000) {  // Check negative sign
        tempData |= 0xC000;  // Sign extend
    }

    return (float)tempData * 0.25;
}
/* USER CODE END PV */

/* Private function prototypes -----------------------------------------------*/
void SystemClock_Config(void);
static void MX_GPIO_Init(void);
static void MX_SPI1_Init(void);
/* USER CODE BEGIN PFP */

/* USER CODE END PFP */

/* Private user code ---------------------------------------------------------*/
/* USER CODE BEGIN 0 */

/* USER CODE END 0 */

/**
  * @brief  The application entry point.
  * @retval int
  */
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 */

  /* USER CODE END 2 */

  /* Infinite loop */
  /* USER CODE BEGIN WHILE */
  while (1)
  {
    /* USER CODE END WHILE */

    /* USER CODE BEGIN 3 */
	  temperature = MAX31855_GetTemperature();
	  HAL_Delay(1000);
  }
  /* USER CODE END 3 */
}

/**
  * @brief System Clock Configuration
  * @retval None
  */
void SystemClock_Config(void)
{
  RCC_OscInitTypeDef RCC_OscInitStruct = {0};
  RCC_ClkInitTypeDef RCC_ClkInitStruct = {0};

  /** Initializes the RCC Oscillators according to the specified parameters
  * in the RCC_OscInitTypeDef structure.
  */
  RCC_OscInitStruct.OscillatorType = RCC_OSCILLATORTYPE_HSE;
  RCC_OscInitStruct.HSEState = RCC_HSE_ON;
  RCC_OscInitStruct.HSEPredivValue = RCC_HSE_PREDIV_DIV1;
  RCC_OscInitStruct.HSIState = RCC_HSI_ON;
  RCC_OscInitStruct.PLL.PLLState = RCC_PLL_ON;
  RCC_OscInitStruct.PLL.PLLSource = RCC_PLLSOURCE_HSE;
  RCC_OscInitStruct.PLL.PLLMUL = RCC_PLL_MUL9;
  if (HAL_RCC_OscConfig(&RCC_OscInitStruct) != HAL_OK)
  {
    Error_Handler();
  }

  /** Initializes the CPU, AHB and APB buses clocks
  */
  RCC_ClkInitStruct.ClockType = RCC_CLOCKTYPE_HCLK|RCC_CLOCKTYPE_SYSCLK
                              |RCC_CLOCKTYPE_PCLK1|RCC_CLOCKTYPE_PCLK2;
  RCC_ClkInitStruct.SYSCLKSource = RCC_SYSCLKSOURCE_PLLCLK;
  RCC_ClkInitStruct.AHBCLKDivider = RCC_SYSCLK_DIV1;
  RCC_ClkInitStruct.APB1CLKDivider = RCC_HCLK_DIV2;
  RCC_ClkInitStruct.APB2CLKDivider = RCC_HCLK_DIV1;

  if (HAL_RCC_ClockConfig(&RCC_ClkInitStruct, FLASH_LATENCY_2) != HAL_OK)
  {
    Error_Handler();
  }
}

/**
  * @brief SPI1 Initialization Function
  *  None
  * @retval None
  */
static void MX_SPI1_Init(void)
{

  /* USER CODE BEGIN SPI1_Init 0 */

  /* USER CODE END SPI1_Init 0 */

  /* USER CODE BEGIN SPI1_Init 1 */

  /* USER CODE END SPI1_Init 1 */
  /* SPI1 parameter configuration*/
  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_128;
  hspi1.Init.FirstBit = SPI_FIRSTBIT_MSB;
  hspi1.Init.TIMode = SPI_TIMODE_DISABLE;
  hspi1.Init.CRCCalculation = SPI_CRCCALCULATION_DISABLE;
  hspi1.Init.CRCPolynomial = 10;
  if (HAL_SPI_Init(&hspi1) != HAL_OK)
  {
    Error_Handler();
  }
  /* USER CODE BEGIN SPI1_Init 2 */

  /* USER CODE END SPI1_Init 2 */

}

/**
  * @brief GPIO Initialization Function
  *  None
  * @retval None
  */
static void MX_GPIO_Init(void)
{
/* USER CODE BEGIN MX_GPIO_Init_1 */
/* USER CODE END MX_GPIO_Init_1 */

  /* GPIO Ports Clock Enable */
  __HAL_RCC_GPIOD_CLK_ENABLE();
  __HAL_RCC_GPIOA_CLK_ENABLE();

/* USER CODE BEGIN MX_GPIO_Init_2 */
/* USER CODE END MX_GPIO_Init_2 */
}

/* USER CODE BEGIN 4 */

/* USER CODE END 4 */

/**
  * @brief  This function is executed in case of error occurrence.
  * @retval None
  */
void Error_Handler(void)
{
  /* USER CODE BEGIN Error_Handler_Debug */
  /* User can add his own implementation to report the HAL error return state */
  __disable_irq();
  while (1)
  {
  }
  /* USER CODE END Error_Handler_Debug */
}

#ifdef  USE_FULL_ASSERT
/**
  * @brief  Reports the name of the source file and the source line number
  *         where the assert_param error has occurred.
  *   file: pointer to the source file name
  *   line: assert_param error line source number
  * @retval None
  */
void assert_failed(uint8_t *file, uint32_t line)
{
  /* USER CODE BEGIN 6 */
  /* User can add his own implementation to report the file name and line number,
     ex: printf("Wrong parameters value: file %s on line %d\r\n", file, line) */
  /* USER CODE END 6 */
}
#endif /* USE_FULL_ASSERT */

[Peter BENSCH]

@asking Your thread was moved here because the Blue and other colourful Pills are neither a product of STMicroelectronics nor use an original MCU from STMicroelectronics, but have only contained counterfeit MCUs for years. There are plenty of similar threads here in the community with similar problems, e.g. here or there.

In this respect, you should contact the manufacturer or the supplier of this Blue Pill.

Regards
/Peter