Single chip microcomputer realizes point-to-point data transmission-serial communication

When the single-chip microcomputer is controlling local peripherals, information exchange is carried out through an 8-bit parallel data bus. However, in larger-scale modern control systems, the single-chip microcomputer also needs to control remote devices. The serial communication module of the single-chip microcomputer can be used. After learning the principles and timing of RS-232 serial communication, we learned to use the RS-232 interface to realize point-to-point communication of serial data transmission.

 

Main components:

1. AT89C52 single-chip microcomputer chip, used to control serial port communication.

2. Interface level conversion chip MAX3232 is used to realize the conversion between TTL level and RS-232 level.

 

Test flow chart: host part                             

 Slave part:

Test circuit diagram:

Test program code:

//PPDataR.h program

#ifndef _PPDATAR_H // Prevent PPDataT.h from being referenced repeatedly

 

#define _PPDATAR_H

 

#include

#include

 

#define uchar unsigned char

#define uint unsigned int

 

/* Handshake signal macro definition */

#define CALL 0x24 // Host call

#define BUSY 0x15 // Slave is busy

#define OK 0x00 // Slave is ready

#define SUCC 0x2A // Receive successfully

#define ERR 0xF0 // Receive error

 

#define MAXLEN 64 // Maximum length of the buffer

 

uchar buf[MAXLEN];

 

#endif

 

//PPDataR.c program

#include "PPDataR.h"

 

/* Send data function */

uchar recvdata(uchar *buf)

{

       uchar i,tmp;

       uchar len; // Save data length

       uchar ecc; // Save the check byte

      

       /* Receive data length bytes */

       RI = 0;

       while(!RI);

       len = SBUF;

       RI = 0;

      

       /* Use the value of len to initialize the check byte ecc */

       ecc = len;                                  

 

       /* Receive data */

       for (i=0;i

       {

              while(!RI);

              *buf = SBUF;    

              ecc = ecc^(*buf); // Perform byte check

              RI = 0;      

              buf++;             

       }

       *buf = 0; // indicates the end of data

      

       /* Receive checksum byte */

       while(!RI);

       tmp = SBUF;

       RI = 0;

 

       /* Perform data verification */

       ecc = tmp^ecc;

       if (ecc!=0) // If the check is wrong

       {

              *(buf-len) = 0; // Clear the data buffer

             

              /* Send verification error signal ERR */

              TI = 0;      

              SBUF = ERR;

              while(!TI);

              TI = 0;

 

              return 0xff; // Return 0xff to indicate verification error

       }

 

       /* Send verification success signal SUCC */

       TI = 0;

       SBUF = SUCC;

       while(!TI);

       TI = 0;

 

       return 0; // Verification successful, return 0

}

 

void init_serial()

{

       TMOD = 0x20; // Timer T1 uses working mode 2

       TH1 = 250;

       TL1 = 250;

       TR1 = 1; // Start timing

       PCON = 0x80; // SMOD = 1

       SCON = 0x50; // Working mode 1, baud rate 9600kbit/s, receiving is allowed

}

 

/* Main program */

void main()

{

       uchar tmp = 0;

       /* Serial port initialization */

       init_serial();

 

       EA = 0; // Disable all interrupts

 

       while(1)

       {

              /* If the received data is not CALL, continue waiting */

              while (tmp!=CALL)

              {

                     RI = 0;

                     while(!RI)

                     tmp = SBUF;

                     RI = 0;

              }

      

              /* Check the P0 port to determine whether it is currently busy. If P0＝0xBB, it is busy */

              P0 = 0xff;

              tmp = P0;

              if(tmp==0xBB) // If the P0 port is 0xBB, send a BUSY signal

              {

                     TI = 0;

                     SBUF = BUSY;

                     while(!TI);

                     TI = 0;

                     continue;

              }

 

              /* Otherwise, send an OK signal, indicating that the slave can receive data */

              TI = 0;                           

              SBUF = OK;

              while(!TI);

              TI = 0;

 

              /* Data receiving */

              tmp = 0xff;

              while(tmp==0xff)

              {

                     tmp = recvdata(buf); // If verification fails, 0xff is returned; if reception succeeds, 0 is returned

              }

       }

}