Discovery L0538 UART2 RX Pin Stuck Low?

[nobbyv77]

Using a Discovery L0538, and want to make use of the 2nd UART (really only need the RX on pin PA3). I noted in the User Manual that to disable the onboard touch sensor and use this pin, I need to jump solder bridge SB24 (which I did, alng with the other five SBs next to it).

However, this pin appears stuck low when I try to receive data on it (all zeroes). I am using a RS232 to TTL converter board to send data to it. If I remove the wire from the converter to PA3, I can see the correct data from the converter board. But as soon as a solder it back to PA3 all I get is zeroes. I config'd the UART with MXCube; note that UART1 is working fine.

Have I missed something else to get this pin working as a UART? I verified with a DMM the solder bridges have continuity. Not detecting a short to ground on PA3. Tried enabling the pullup on that pin, no change.

[Tesla DeLorean]

Pull a schematic from the "CAD Resources" tab, and trace the signal path

[waclawek.jan]

From schematics it appears that PA3 has a fixed connection to C14/47nF. This is not ideal, but shouldn't cause the symptom you describe.

Try to write a simple code which sets PA3 as GPIO input, a suitable pin as GPIO output, and do nothing just move in a loop level of PA3 to that output pin, and then check using oscilloscope.

If this works, your setup is wrong, it does not matter that you've clicked it in CubeMX. Read out and check/post content of USART and relevant GPIO registers.

JW

[nobbyv77]

I am absolutely stumped. I created a new project w/ no UART, just the one active GPIO in question (PA3) that I toggle. Works fine, so no shorts on the pin. Started a new project w/ nothing else besides the two UARTS, both init'd as per CubeMX. Swapped the output of the RS232/TTL converter between UART1 and UART2. UART1 works perfectly fine. UART2 only captures zereos. The init code is IDENTICAL. What could I possibly be missing? 

Clock init including periph clocks:
 
void SystemClock_Config(void)
{
  RCC_OscInitTypeDef RCC_OscInitStruct = {0};
  RCC_ClkInitTypeDef RCC_ClkInitStruct = {0};
  RCC_PeriphCLKInitTypeDef PeriphClkInit = {0};
 
  /** Configure the main internal regulator output voltage
  */
  __HAL_PWR_VOLTAGESCALING_CONFIG(PWR_REGULATOR_VOLTAGE_SCALE1);
 
  /** Initializes the RCC Oscillators according to the specified parameters
  * in the RCC_OscInitTypeDef structure.
  */
  RCC_OscInitStruct.OscillatorType = RCC_OSCILLATORTYPE_HSI;
  RCC_OscInitStruct.HSIState = RCC_HSI_ON;
  RCC_OscInitStruct.HSICalibrationValue = RCC_HSICALIBRATION_DEFAULT;
  RCC_OscInitStruct.PLL.PLLState = RCC_PLL_ON;
  RCC_OscInitStruct.PLL.PLLSource = RCC_PLLSOURCE_HSI;
  RCC_OscInitStruct.PLL.PLLMUL = RCC_PLLMUL_6;
  RCC_OscInitStruct.PLL.PLLDIV = RCC_PLLDIV_3;
  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_DIV1;
  RCC_ClkInitStruct.APB2CLKDivider = RCC_HCLK_DIV1;
 
  if (HAL_RCC_ClockConfig(&RCC_ClkInitStruct, FLASH_LATENCY_1) != HAL_OK)
  {
    Error_Handler();
  }
  PeriphClkInit.PeriphClockSelection = RCC_PERIPHCLK_USART1|RCC_PERIPHCLK_USART2;
  PeriphClkInit.Usart1ClockSelection = RCC_USART1CLKSOURCE_PCLK2;
  PeriphClkInit.Usart2ClockSelection = RCC_USART2CLKSOURCE_PCLK1;
  if (HAL_RCCEx_PeriphCLKConfig(&PeriphClkInit) != HAL_OK)
  {
    Error_Handler();
  }
}

UART Init'ing:

* @brief USART1 Initialization Function
  * @param None
  * @retval None
  */
static void MX_USART1_UART_Init(void)
{
  huart1.Instance = USART1;
  huart1.Init.BaudRate = 57600;
  huart1.Init.WordLength = UART_WORDLENGTH_8B;
  huart1.Init.StopBits = UART_STOPBITS_1;
  huart1.Init.Parity = UART_PARITY_NONE;
  huart1.Init.Mode = UART_MODE_TX_RX;
  huart1.Init.HwFlowCtl = UART_HWCONTROL_NONE;
  huart1.Init.OverSampling = UART_OVERSAMPLING_16;
  huart1.Init.OneBitSampling = UART_ONE_BIT_SAMPLE_DISABLE;
  huart1.AdvancedInit.AdvFeatureInit = UART_ADVFEATURE_NO_INIT;
  if (HAL_UART_Init(&huart1) != HAL_OK)
  {
    Error_Handler();
  }
}
 
/**
  * @brief USART2 Initialization Function
  * @param None
  * @retval None
  */
static void MX_USART2_UART_Init(void)
{
  huart2.Instance = USART2;
  huart2.Init.BaudRate = 57600;
  huart2.Init.WordLength = UART_WORDLENGTH_8B;
  huart2.Init.StopBits = UART_STOPBITS_1;
  huart2.Init.Parity = UART_PARITY_NONE;
  huart2.Init.Mode = UART_MODE_TX_RX;
  huart2.Init.HwFlowCtl = UART_HWCONTROL_NONE;
  huart2.Init.OverSampling = UART_OVERSAMPLING_16;
  huart2.Init.OneBitSampling = UART_ONE_BIT_SAMPLE_DISABLE;
  huart2.AdvancedInit.AdvFeatureInit = UART_ADVFEATURE_NO_INIT;
  if (HAL_UART_Init(&huart2) != HAL_OK)
  {
    Error_Handler();
  }
}

UART hardware init:

/**
* @brief UART MSP Initialization
* This function configures the hardware resources used in this example
* @param huart: UART handle pointer
* @retval None
*/
void HAL_UART_MspInit(UART_HandleTypeDef* huart)
{
  GPIO_InitTypeDef GPIO_InitStruct = {0};
  if(huart->Instance==USART1)
  {
    /* Peripheral clock enable */
    __HAL_RCC_USART1_CLK_ENABLE();
 
    __HAL_RCC_GPIOA_CLK_ENABLE();
    /**USART1 GPIO Configuration
    PA9     ------> USART1_TX
    PA10     ------> USART1_RX
    */
    GPIO_InitStruct.Pin = GPIO_PIN_9|GPIO_PIN_10;
    GPIO_InitStruct.Mode = GPIO_MODE_AF_PP;
    GPIO_InitStruct.Pull = GPIO_NOPULL;
    GPIO_InitStruct.Speed = GPIO_SPEED_FREQ_VERY_HIGH;
    GPIO_InitStruct.Alternate = GPIO_AF4_USART1;
    HAL_GPIO_Init(GPIOA, &GPIO_InitStruct);
 
    /* USART1 interrupt Init */
    HAL_NVIC_SetPriority(USART1_IRQn, 0, 0);
    HAL_NVIC_EnableIRQ(USART1_IRQn);
  }
  else if(huart->Instance==USART2)
  {
    /* Peripheral clock enable */
    __HAL_RCC_USART2_CLK_ENABLE();
 
    __HAL_RCC_GPIOA_CLK_ENABLE();
    /**USART2 GPIO Configuration
    PA2     ------> USART2_TX
    PA3     ------> USART2_RX
    */
    GPIO_InitStruct.Pin = GPIO_PIN_2|GPIO_PIN_3;
    GPIO_InitStruct.Mode = GPIO_MODE_AF_PP;
    GPIO_InitStruct.Pull = GPIO_NOPULL;
    GPIO_InitStruct.Speed = GPIO_SPEED_FREQ_VERY_HIGH;
    GPIO_InitStruct.Alternate = GPIO_AF4_USART2;
    HAL_GPIO_Init(GPIOA, &GPIO_InitStruct);
 
    /* USART2 interrupt Init */
    HAL_NVIC_SetPriority(USART2_IRQn, 0, 0);
    HAL_NVIC_EnableIRQ(USART2_IRQn);
  }
}

Does anyone see any difference between these two?

[waclawek.jan]

Read out and check/compare to working/post content of USART and relevant GPIO registers.

JW

[nobbyv77]

I'm no sure what you mean. I am comparing working USART content, it looks identical to the non-working content, but no joy between them.

[waclawek.jan]

In debugger, read out USART registers and GPIOA registers, and post what you read out.

JW

[jvavra]

This is the contents of the GPIOA and UART2 registers when I am receiving all zeroes on UART2. I set a breakpoint in the HAL_UART_Receive_IT routine just before the function returns.

[waclawek.jan]

Hi @Community member​  ,

I am confused. Are you co-worker of of @Community member​ , is this the same hardware/software as he is describing above?

JW

[jvavra]

My apologies: when I left an earlier job, I had to create a new ST account as I was not able to access my old work email. Looks like I inadventantly logged in with the old one. Same guy though!