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

[AStar.4]

I am a new member, I am learning about UART data transmission of MCU STM32F411RE on a nucleon board. I have read and understood the function HAL_UART_Transmit. However, in this function, there is a part I don't understand. I don't understand the meaning of the program below:

if (huart->Init.WordLength == UART_WORDLENGTH_9B)

     {

       if (UART_WaitOnFlagUntilTimeout(huart, UART_FLAG_TXE, RESET, tickstart, Timeout) != HAL_OK)

       {

         return HAL_TIMEOUT;

       }

       tmp = (uint16_t *) pData;

       huart->Instance->DR = (*tmp & (uint16_t)0x01FF);

       if (huart->Init.Parity == UART_PARITY_NONE)

       {

         pData += 2U;

       }

       else

       {

         pData += 1U;

       }

     }

In the 9-Bit frame mode, why after each assignment of data from the pData pointer to the DR register:

- pData += 2U if Parity = PARITY_NONE

- pData += 1U if Parity != PARITY_NONE

As I understand it, after: tmp = (uint16_t *) pData;

                       huart->Instance->DR = (*tmp & (uint16_t)0x01FF);

Then the pointer will be incremented by 1 to assign the next memory area to DR. So why is there a case where the pData pointer grows to 2U. If so, is it possible that the transmitted data will be wrong?

Hope everyone can answer. Thank you.

[TDK]

If you are sending 9 bits of data, you must store each value in a uint16_t which takes 2 bytes. Since pData is of type uint8_t*, in order to increment it to the next value, the pointer must increase by 2.

If you are sending 9 bits, but only 8 of them are data and 1 is parity, the data fits in a uint8_t which is one byte.

[AStar.4]

Dear @TDK​ , thank you for your reply. Your answer helped me understand the essence of the problem.

I would like to review my understanding as below:

If I want to send 9 Bit data, I need to declare and transfer to the function a 2 Byte Data(uint16_t)

Since the pData pointer declared in the function is 8 Bit (uint8_t), it is necessary to increase pData by 2U to correctly point at the next location of the data area

For example, if I want to pass an Array: uint16_t Data_9Bit[2] = {0x1AB, 0x1FF};

So, the transmitted data will be guaranteed to be correct and accurate.

[TDK]

Correct. You would need to convert the pointer to uint8_t * to call the function.

HAL_UART_Transmit(huart, (uint8_t *) Data_9Bit, 2, timeout);