51 MCU and PC serial port asynchronous communication continued

The main function of the following program is to send a letter to the 51 single-chip microcomputer through the serial port debugging assistant. After the single-chip microcomputer receives it, it displays the letter on the digital tube and displays the letter in reverse in the interface of the serial port debugging assistant.

A series of special function registers such as serial port buffer have been defined in the header file of 51 single chip microcomputer. You can find the following definition by opening the header file:

sfr SCON = 0x98;
sfr SBUF = 0x99;

etc.

First, create a new header file and write the variable and function declarations to be used in the program:

#include 
#include 

#define uchar unsigned char

sbit dula=P2^6;
sbit wela=P2^7;

//Letters sent from the computer to the microcontroller
uchar letter;

//The table array stores the codes corresponding to the digital tube display 0~F
//Only A~F are used here
uchar code table[]={
0x3f,0x06,0x5b,0x4f,
0x66,0x6d,0x7d,0x07,
0x7f,0x6f,0x77,0x7c,
0x39,0x5e,0x79,0x71};

void Inital();
void Display(uchar mydata);
void Putchar(uchar mydata);
void ShortDelay();

The main purpose of including the header file is to use the library function toupper() to convert the read letters into uppercase, making it easier to call the Display function to display them on the digital tube.

The main function is very simple. It first initializes and then enters a loop that is always true, waiting for the interrupt to occur and processing it.

void main()
{
  Inital(); // Initialization
  while(1)  
  {
  }
}

The initialization function is used to enable interrupts, set timers, serial communication working mode, and variable initialization:

void Inital()
{
  // Clear the variable
  letter=0;
  wela=0;
  dula=0;
 
  //Set the baud rate to 9600
  SCON=0x50;
  TMOD=0x20;
  TH1=0xfd;
  TL1=0xfd;
  TR1=1;
 
  //Open serial port interrupt
  EA=1;
  ES=1;
}

The interrupt service function is called by the CPU when an interrupt occurs, and Display is called inside it. The Putchar function is used to display letters on the digital tube and echo the input letters on the computer.

//Interrupt service function
void ser() interrupt 4
{
  //If you have finished reading the data
  if(RI==1)
  {
    RI=0; //software clear
    letter=SBUF; //Read data from the MCU Receive buffer
    Putchar(letter); //Echo letter on the computer
    Display(letter); //Display the corresponding letter on the digital tube
  }
}

The Display function is only used in the previous article about digital tubes. Here is the code directly:

void Display(uchar mydata)  
{
  uchar BigLetter;  
  BigLetter=toupper(mydata); //First convert all the letters read into uppercase so that they can be processed uniformly
  
  //Digital selector tube
  wela=1;
  P0=0xfb;
  wela=0;
  
  P0=0xff;
  
  //Segment selection
  //BigLetter-'A'+10 index is the subscript of the letter in the table
  dula=1;
  P0=table[BigLetter-'A'+10];
  dula=0;
  ShortDelay();
}

void ShortDelay()
{
  uchar a=100;
  while(a--);
}

Putchar function to send information to the computer

void Putchar(uchar mydata)
{
  SBUF=mydata; //Write data into the transfer buffer of the microcontroller
  while(!TI); //Is the sending finished?
  TI=0; //software clears after sending
}

In this way, you can use the serial port debugging assistant to send letters to the microcontroller, display the letters on the digital tube, and display the content of the letters just sent on the software interface.