Serial communication between 51 microcontroller and PC

The serial port control register of the microcontroller is SCON, and its format is as follows:

The serial port has four working modes, namely 00, 01, 10, and 11. Mode 0 is a synchronous shift register, and modes 1, 2, and 3 are asynchronous 10, 11, and 11-bit transceiver modes. Mode 1, i.e. 10-bit asynchronous transceiver mode, is commonly used.

The specific analysis of the 10-bit data transmission and reception of mode 01 is as follows:

The data to be sent is SBUF=0X34. According to the waveform, the 10-bit data has a start bit of 1 (not marked on the waveform here), and the last bit is 1. The middle bit is 8-bit data 00110100 (0x34). When the 8th bit is sent, the MCU automatically sends an end flag, that is, sets TI to 1. Setting TI to 1 indicates that the data has been sent. TI cannot be automatically cleared, so it needs to be cleared by software after each data is sent: 

As above, when the microcontroller needs to receive data, it also executes the same steps. First, it receives 8 bits of data, and then sets the receiving flag RI to 1.

The initialization steps of the serial port are mainly to set the timer 1 that generates the baud rate, the serial port control box interrupt control, the steps are as follows:

Code:

//Serial port initialization program

TMOD&=0x0f;

TMOD|=0x20;

TH1=0XFD; //Set the baud rate to 9600

TL1=0xFD;

TR1=1; //Start timer T1

SCON=0X50; //10-bit data is sent and received asynchronously, the baud rate is controlled by timer T1, allowing serial port reception

  ES=1; //Enable serial port interrupt

    //Serial port initialization completed

Below I wrote a program for serial port communication with PC:

#include

unsigned char flag,i;

unsigned int k,j;

unsigned char a[32]={0};

unsigned char code table[6]="I get ";

void init()

{

 TMOD=0x20; //Set timer working mode 2

 TH1=0xfd; //Load initial value into timer 1

 TL1=0xfd; //same as above

 TR1=1; //Start T1 timer

 SM0=0; //Set working mode 1

 SM1=1; //same as above

 REN=1; // Allow serial port to receive

 EA=1; //Open the general interrupt

 ES=1; //Open serial port interrupt

}

void main()

{

 init();

 while(1)

 {

  if(flag==1)

  {

   ES=0;

   for(i=0;i<6;i++)

   {

    SBUF=table[i];

    while(!TI);

    TI=0;

   }

   ES=1;

  for(k=0;k<0xFFFF;k++);

  for(i=0;i<32;i++)

   {  

   SBUF=a[i];           

   while(!TI);

   TI=0;

   }

   flag=0;

  } 

 }  

}

void ser() interrupt 4 //interrupt program, receive data block, flag position 1

{   

flag=1;

if(RI==1){

a[j++]=SBUF;

   RI=0; //Manual clear  

}

}

The serial communication effect is as follows:

But there is a small problem with my program. I have tried many ways to solve it, but all failed. When the data I input is greater than 2 bytes, it can only return the first two bytes of data. As shown below: