Reasons and solutions for the loss of the first character of a string sent by USART-EEWORLD

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When writing the sending code with reference to the official USART example, the first character of the string is inexplicably lost

/* eg write a character to the USART */

USART_SendData(EVAL_COM1, (uint8_t) ch);

/* Loop until the end of transmission */

while (USART_GetFlagStatus(EVAL_COM1, USART_FLAG_TC) == RESET)

{}

After looking through the data sheet, I found that the TXE and TC flags are set to 1 by default after reset, which causes the first flag detection to fail and the first character is overwritten before it is sent.

[STM32] Causes and solutions for the loss of the first character of a string sent by USART - rainsmell - rainsmells blog

Once the cause is found, the solution is quite simple. Just clear the flag bit before sending the first character.

Two methods:

1. Change the TC detection to the TXE inspection

while (USART_GetFlagStatus(EVAL_COM1, USART_FLAG_TXE) == RESET)

2. Before writing data to the USART_DR register, read the USART_SR register once

/* Read USART_SR register */ USARTx -> SR; /* eg write a character to the USART */ USART_SendData(EVAL_COM1, (uint8_t) ch); /* Loop until the end of transmission */ while (USART_GetFlagStatus(EVAL_COM1, USART_FLAG_TC ) == RESET) {}

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