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Little knowledge about TXE and TC flag bits

2022-07-08 02:03:00 【51CTO】

TXE Sign a

（ in the light of Send data register ）

TXE by 1：TDR All the data in is moved to the shift register , And no new data into TDR.

TXE by 0：TDR There are data in it. , Not empty , be TXE by 0.

TXE And "FlagStatus USART_GetFlagStatus(USART_TypeDef* USARTx, uint16_t USART_FLAG)" Use it together to judge TDR Whether there is data in

       
       int 
       
       main (
       
       void){
       
       My_ 
       
       _USART1() ;
       
       USART_SendData (
       
       USART1,
       
       'H');
       
       while (
       
       USART_GetFlagStatus( 
       
       USART1, 
       
       USART_FLAG_TXE) 
       
       == 
       
       RESET);
       
       USART_SendData (
       
       USART1,’K
       
       ');
       
       while (
       
       USART_GetFlagStatus ( 
       
       USART1, 
       
       USART_FLAG_TXE) 
       
       == 
       
       RESET);
       
       USART_SendData (
       
       USART1,” 
       
       G
       
       ');
       
       while (
       
       USART_GetFlagStatus( 
       
       USART1, 
       
       USART_FLAG_TXE) 
       
       == 
       
       RESET);
       
       while(
       
       1){}
       
}
       
       // Output ：H K G
      
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TC Sign a

（ in the light of Send data register ）

TC by 1： from TDR All the data coming over are transferred to TX Pin , And TDR There is no new data in .

TC by 0： from TDR All the data in has not been moved , Or before TDR The data in has been removed , but TDR New data is coming in .

       
       int 
       
       main (
       
       void){
       
       My_ 
       
       _USART1() ;
       
       USART_SendData (
       
       USART1,
       
       'H');
       
       while (
       
       USART_GetFlagStatus( 
       
       USART1, 
       
       USART_FLAG_TC) 
       
       == 
       
       RESET);
       
       USART_SendData (
       
       USART1,’K
       
       ');
       
       while (
       
       USART_GetFlagStatus ( 
       
       USART1, 
       
       USART_FLAG_TC) 
       
       == 
       
       RESET);
       
       USART_SendData (
       
       USART1,” 
       
       G
       
       ');
       
       while (
       
       USART_GetFlagStatus( 
       
       USART1, 
       
       USART_FLAG_TC) 
       
       == 
       
       RESET);
       
       while(
       
       1){}
       
}
       
       // Output ：K G
      
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The reason lies in

About TXE and TC Little knowledge of flag bits _TC

       
       // The first 10/11 The execution is to write DR, Read again SR, The steps are just the opposite , that TC The flag bit is not clear 0
       
       // Because it is not equal to RESET, So I will immediately execute the next line , Now "K" Will “H” overwrite 
       
       // Sending in execution "G" The operations in the above figure have been performed when , The relevant conditions are met 
      
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resolvent ：

Sending "K" Read first USART_SR;

       
       int 
       
       main (
       
       void){
       
       My_USART1() ;
       
       while (
       
       USART_GetFlagStatus( 
       
       USART1, 
       
       USART_FLAG_TC) 
       
       == 
       
       RESET);
       
       USART_SendData (
       
       USART1,
       
       'H');
       
       while (
       
       USART_GetFlagStatus( 
       
       USART1, 
       
       USART_FLAG_TC) 
       
       == 
       
       RESET);
       
       USART_SendData (
       
       USART1,’K
       
       ');
       
       while (
       
       USART_GetFlagStatus ( 
       
       USART1, 
       
       USART_FLAG_TC) 
       
       == 
       
       RESET);
       
       USART_SendData (
       
       USART1,” 
       
       G
       
       ');
       
       while (
       
       USART_GetFlagStatus( 
       
       USART1, 
       
       USART_FLAG_TC) 
       
       == 
       
       RESET);
       
       while(
       
       1){}
       
}
      
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Software clearance “0”, You need to use the following function

       
       // Clear flag bits 
       
       void 
       
       USART_ClearFlag(
       
       USART_TypeDef
       
       * 
       
       USARTx, 
       
       uint16_t 
       
       USART_FLAG);
      
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       int 
       
       main (
       
       void){
       
       My_USART1() ;
       
       USART_ClearFlag(
       
       USART1, 
       
       uint16_t 
       
       USART_FLAG);
       
       USART_SendData (
       
       USART1,
       
       'H');
       
       while (
       
       USART_GetFlagStatus( 
       
       USART1, 
       
       USART_FLAG_TC) 
       
       == 
       
       RESET);
       
       USART_SendData (
       
       USART1,’K
       
       ');
       
       while (
       
       USART_GetFlagStatus ( 
       
       USART1, 
       
       USART_FLAG_TC) 
       
       == 
       
       RESET);
       
       USART_SendData (
       
       USART1,” 
       
       G
       
       ');
       
       while (
       
       USART_GetFlagStatus( 
       
       USART1, 
       
       USART_FLAG_TC) 
       
       == 
       
       RESET);
       
       while(
       
       1){}
       
}
      
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Multiple groups for transmission , You need to view the corresponding multiple TXE Flag bit and a TC Sign a （TC To ensure that the last character is sent from the shift register to TX）

rewrite USART_SendByte() Make it possible to write multiple characters repeatedly

       
       void 
       
       USART_SendByte(
       
       USART_TypeDef
       
       * 
       
       USARTx, 
       
       uint8_t 
       
       Data){
       
       assert_param(
       
       IS_USART_ALL 
       
       PERIPH(
       
       USARTx));
       
       assert_param(
       
       IS_USART_DATA(
       
       Data));
       
       USARTx
       
       ->
       
       DR 
       
       = (
       
       Data 
       
       & (
       
       uint16_t)
       
       0x01FF);
       
       while (
       
       USART_GetFlagStatus(
       
       USARTx, 
       
       USART_FLAG_TXE) 
       
       == 
       
       RESET);
       
}
      
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Function to send string

       
       void 
       
       USART 
       
       SendString( 
       
       USART_TypeDef 
       
       * 
       
       USARTx, 
       
       char 
       
       *
       
       str){
       
       while(
       
       *
       
       str
       
       !=
       
       '\0'){
       
       USART_SendByte( 
       
       USARTx, 
       
       *
       
       str
       
       ++ ); 
       
       while(
       
       USART_GetFlagStatus(
       
       USARTx,
       
       USART_FLAG_TC)
       
       ==
       
       RESET);
       
  }
       
}
      
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Serial communication mode ： Polling 、 Interruption method . Generally, receive and use interrupts .

ITStatus The value is 1, Indicates that the value can be read

ITStatus The value is 0, Indicates that the value cannot be read

Can pass while and if To judge

	USART_GetITStatus()	USART_GetFlagStatus()
The same thing	All access serial ports SR Status register
Difference	It will not only judge whether the flag bit is set 1, It also determines whether the corresponding interrupt is enabled , So interrupt the function in the serial port , This function is usually used	Only the flag bit is judged , When the corresponding interrupt is not enabled , This function is usually used to determine whether the flag bit is set 1.

Understand a library function , It needs to be combined with specific examples .

       
       // It will not only judge whether the flag bit is set 1, It also determines whether the corresponding interrupt is enabled , So interrupt the function in the serial port , This function is usually used 
       
       ITStatus 
       
       USART_GetITStatus(
       
       USART_TypeDef
       
       * 
       
       USART1,
       
       uint16_t 
       
       USART_IT);
      
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printf function

stay C Language is used to print information to the console .printf It is a sharp tool for debugging in the development of MCU ！

Yes printf The underlying function redirects , Use fputc and fgetc

       
       #include "stdio.h"
       
       //fputc and fgetc yes C The standard function of language 
       
       // To use its FILE *f
       
       // Redirect c Library function printf To serial port , After resetting, you can use printf function 
       
       int 
       
       fputc(
       
       int 
       
       ch, 
       
       FILE 
       
       *
       
       f){
       
       USART_SendData (
       
       USART1,(
       
       uint8_t) 
       
       ch);
       
       while (
       
       USART_GetFlagStatus (
       
       USART1,USART_FLAG_TXE) 
       
       == 
       
       RESET);
       
       return (
       
       ch);
       
}
       
       // Redirect c Library function scanf To serial port , Override backward to use scanf、getchar etc.   function 
       
       int 
       
       fgetc(
       
       FILE 
       
       *
       
       f){
       
       while (
       
       USART_GetFlagStatus (
       
       USART1,USART_FLAG_RXNE) 
       
       == 
       
       RESET);
       
       return (
       
       int)
       
       USART_ReceiveData (
       
       USART1);
       
}
      
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printf() Function uses semi host mode , Will cause the program to fail to run , Therefore, this mode should be prohibited

Use Micro Library ： When using the micro Library , Half host mode is turned off by default

Using microlibraries
introduce stdio.h The header file
rewrite fputc and fgetc function

About TXE and TC Little knowledge of flag bits _TXE_02

There may be "FIFLE" is underfined, add

       
       // stay usart.h writes 
       
       typedef 
       
       struct 
       
       __FILE 
       
       FILE
      
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Do not use micro Libraries , But the following words need to be added

       
       #include "stdio.h"
       
       #pragma import(__use_no_semihousting)
       
       struct 
       
       __FILE
       
{
       
       int 
       
       handle;
       
};
       
       FILE 
       
       __stdout;
       
       _sys_exit(
       
       int 
       
       x)
       
{
       
       x 
       
       = 
       
       x;
       
}
       
       // Redirect c Library function printf To serial port , After resetting, you can use printf function 
       
       int 
       
       fputc(
       
       int 
       
       ch, 
       
       FILE 
       
       *
       
       f){
       
       USART_SendData (
       
       USART1,(
       
       uint8_t) 
       
       ch);
       
       while (
       
       USART_GetFlagStatus (
       
       USART1,USART_FLAG_TXE) 
       
       == 
       
       RESET);
       
       return (
       
       ch);
       
}
       
       // Redirect c Library function scanf To serial port , Override backward to use scanf、getchar etc.   function 
       
       int 
       
       fgetc(
       
       FILE 
       
       *
       
       f){
       
       while (
       
       USART_GetFlagStatus (
       
       USART1,USART_FLAG_RXNE) 
       
       == 
       
       RESET);
       
       return (
       
       int)
       
       USART_ReceiveData (
       
       USART1);
       
}
      
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The two methods are the same ：

1 All use “stdio.h" The header file
All need to be rewritten printf The underlying function ,fputs and fgets.

The differences between the two methods ：

Check... Or not “Use MicroLIB”

Semi host mode ： The half host mode is ARM A debugging mechanism of single chip microcomputer , It needs an emulator to connect the computer and ARM Single chip microcomputer , And call the corresponding instructions to realize the MCU to print information to the computer display .

The micro library is designed for small memory embedded devices , It can reduce the space occupied by code .

Minimize the use of micro libraries

be relative to C For the standard library , Fewer functions are supported , Mainly reflected in the support of the operating system .
Standard things are relatively more reliable .

difference	int fputc(int ch,FILE *fp) function	int fgetc(FILE *fp) function
function	Write a character to a file	Read a character from the file
Parameters	ch Characters to write ,fp Point to FILE Pointer to structure	fp Point to FILE Pointer to structure
Return value	success , Returns the character ; When encountering end of file or reading error , return EOF（-1）	success , Returns the character ; When encountering end of file or reading error , return EOF（-1）

当前位置：网站首页>Little knowledge about TXE and TC flag bits

Little knowledge about TXE and TC flag bits

TXE Sign a

TC Sign a

printf function

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