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Samiot
Samiot
Associate
February 6, 2020
Question

UART trames are not good

  • February 6, 2020
  • 1 reply
  • 1878 views

Hello I am worcking an the P-NUCLEO-WB55 and I try to communicate with a other module with the LPUART. Seeing that I didn't have any responce to my commands, I use a scope to see the TX trame.

0690X00000D88KlQAJ.jpgThis is for example the trame of '<' (00111100) .

I used the command HAL_UART_Transmit(&hlpuart1, '<', 1, HAL_MAX_DELAY);

And there, the LPUART parameters:

static void MX_LPUART1_UART_Init(void)

{

 /* USER CODE BEGIN LPUART1_Init 0 */

 /* USER CODE END LPUART1_Init 0 */

 /* USER CODE BEGIN LPUART1_Init 1 */

 /* USER CODE END LPUART1_Init 1 */

 hlpuart1.Instance = LPUART1;

 hlpuart1.Init.BaudRate = 115200;

 hlpuart1.Init.WordLength = UART_WORDLENGTH_8B;

 hlpuart1.Init.StopBits = UART_STOPBITS_1;

 hlpuart1.Init.Parity = UART_PARITY_NONE;

 hlpuart1.Init.Mode = UART_MODE_TX_RX;

 hlpuart1.Init.HwFlowCtl = UART_HWCONTROL_NONE;

 hlpuart1.Init.OneBitSampling = UART_ONE_BIT_SAMPLE_DISABLE;

 hlpuart1.Init.ClockPrescaler = UART_PRESCALER_DIV1;

 hlpuart1.AdvancedInit.AdvFeatureInit = UART_ADVFEATURE_NO_INIT;

 hlpuart1.FifoMode = UART_FIFOMODE_DISABLE;

 if (HAL_UART_Init(&hlpuart1) != HAL_OK)

 {

  Error_Handler();

 }

 if (HAL_UARTEx_SetTxFifoThreshold(&hlpuart1, UART_TXFIFO_THRESHOLD_1_8) != HAL_OK)

 {

  Error_Handler();

 }

 if (HAL_UARTEx_SetRxFifoThreshold(&hlpuart1, UART_RXFIFO_THRESHOLD_1_8) != HAL_OK)

 {

  Error_Handler();

 }

 if (HAL_UARTEx_DisableFifoMode(&hlpuart1) != HAL_OK)

 {

  Error_Handler();

 }

 /* USER CODE BEGIN LPUART1_Init 2 */

 /* USER CODE END LPUART1_Init 2 */

}

I tired to send many other caracters but I never see the good trame on the scope.

Any idea of what appened?

This topic has been closed for replies.

1 reply

Danish1
Danish1
Lead III
February 6, 2020

I think HAL_UART_Transmit needs a C string "<" not a single character '<'.

Hope this helps,

Danish

Samiot
SamiotAuthor
Associate
February 6, 2020

Well not really but thanks for the advice

Danish1
Danish1
Lead III
February 6, 2020

You might have some other things wrong, but when you call

HAL_UART_Transmit(&hlpuart1, '<', 1, HAL_MAX_DELAY);

what the library-function is expecting is of the form

HAL_StatusTypeDef HAL_UART_Transmit(UART_HandleTypeDef *huart, uint8_t *pData, uint16_t Size, uint32_t Timeout);

So you are giving '<' to the pointer-to-string variable pData.

What does the C compiler do under these circumstances?

It gets the ascii value of the character '<', in this case 0b00111100 or 0x3c

And passes that as the address for where to find the (in your case one-character) string.

And then the library-function then sends whatever happens to be in memory location 0x3c. Not the value 0x3c.

If instead you did

HAL_UART_Transmit(&hlpuart1, "<", 1, HAL_MAX_DELAY);

The C compiler would create a C string consisting of your character '<' and the string-terminator '\0' and store it in program memory. It would pass the address of that string to HAL_UART_Transmit(). And the library-function would look in the memory-location specified by the address, and retrieve the character '<' and send it.

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