Scoring system based on 485 bus

Practical tasks

B Level task （80%）                     

requirement ：

    Use two STC Download the provided in the previous section .hex file , build 485 Dual computer communication circuit , stay linux Program code for scoring in .       

step ：

1. Read the flow chart of the program system , Clarify the functional requirements of dual computer communication .

2. Be familiar with the simulation in the previous section MODBUS Packet structure of the protocol , Relevant function codes and additional data definitions

   | Function code          | Read the function code of the lower computer | 0X03 |

   | -------------- | -------------- | ---- |

   | Detect function code      | 0X08           |      |

   | Address error function code | 0X10           |      |

   | Reset function code      | 0X01           |      |

   | Additional data        | Error code          | 0X6F |

   | baotou            | 0X5A           |      |

   | Broadcast address        | 0X00           |      |

   | Custom content      | 0X13           |      |

   Check bytes in the Protocol , This scoring system adopts accumulation and coding .

3. review 485 Bus data transceiver experiment , Build a dual computer communication circuit . Refer to the previous section to ensure STC After setting the slave number and score , Press down KEY2、KEY3 Key symbol , The first 1 Position and number 8 position LED The light is on .

4. PC The end serial port settings are as follows ：

   Serial port baud rate ：9600 Data bits ：8 position   Check bit ： nothing Stop bit ：1

5. Written PC The end program should complete a complete scoring process by referring to the communication protocol in the previous section ：

- - You need to include the settings of the serial port

  - The master node initiates the slave detection process ： Send the normal detection packet of the specified slave number , Judge whether the response query packet conforms to the communication protocol in the previous section .

  - The master obtains the scoring process of the slave ： Send the data package related to the specified slave scoring , Judge whether the response query packet conforms to the communication protocol in the previous section .

  - The host initiates the process of ending the scoring , If reset succeeds ,STC From the plane 1 Position and number 8 position LED The light will go out .

  - Display serial port related information , Display the detected slave number and the score of the slave .

Code design

#include <cstdio>
#include <iostream>
#include <string>
#include <unistd.h>
#include <signal.h>
#include "serial.h"
#include <setjmp.h>
using namespace std;
typedef unsigned char uchar;


/*  be based on RS485 Bus scoring system - Host program - Double machine scoring  */
string format(const vector<uchar> &data);			// Data is processed into strings 
int check(serial &pipe, int addr);				// Equipment inspection 
int get_score(serial &pipe, int addr);			// Get points 
void reset(serial &pipe);					// Slave reset 

int main() {
    serial pipe("/dev/ttyUSB0", B9600);
    int addr, check_ret, score;
    while(1){
        cout<<" Enter description ：\n Enter the legal slave address to query the score \n Input -2 Reset the slave \n Input -1 Exit procedure \n If the program does not work correctly , Cannot receive slave response , Please restart and try again \n Please enter the command ：";
        cin>>addr;
        if(addr == -1) break;
        if(addr == -2) {
            reset(pipe);
            continue;
        }
        check_ret = check(pipe, addr);
        if(check_ret == 1){
            cout<<" Equipment detection is normal "<<endl;
            sleep(1);
    	    if(!(score = get_score(pipe, addr)))
    	        cout<<" Failed to get score "<<endl;
    	    else 
    	        cout<<" fraction ："<<score<<endl;
        }
        else if(check_ret == 0){
            cout<<" Wrong address , Please enter the address and try again "<<endl;
            continue;
        }
	else{
	    cout<<" Data transmission error , Please restart the slave "<<endl;
	}        

        //reset(pipe);
        cout<<" The slave has been reset , Input -1 sign out "<<endl;
    }
    return 0;

}
/***************************************************** 
 Process data into strings 
******************************************************/
string format(const vector<uchar> &data) {
    std::string str(2 * data.size() + 1, '\x00');
    for (int i = 0; i < data.size(); i++) {
        sprintf(&str[i * 2], "%02X", data[i]);
    }
    return str;
}
/***************************************************** 
 Slave address detection ：
 Parameters ：serial A serial port , Slave address 
 The host sends data for detection ：5a +  Slave address  +  Detect function code 08 + 13 +  Check code  
 Return value ：1( The address is correct );0( Wrong address );-1( Data error )
******************************************************/
int check(serial &pipe,int addr){
	int check_code = 117 + addr, ret;				// The check code is cumulative sum 
	vector<uchar> code = {0x5a, 0x08, 0x13};
	vector<uchar> rec;
	code.insert(code.begin()+1, (uchar)addr);			// Insert slave address 
	code.push_back((uchar)check_code);				// Insert the check code 
	//cout << format(code) << endl;				
	

	/*  Write and receive response packets  */
	pipe.myWrite(code);
	sleep(1);
	rec = pipe.myRead(5);
	if(format(rec) == format(code))				// Check whether the received packet is the same as the sent one , If it is the same, the slave address is correct 
	    ret = 1;
	else{
	    if(rec[3] == 0x6f) ret = 0;
	    else ret = -1;
	}
	return ret;

}
/***************************************************** 
 Get slave scores ：
 Parameters ：serial A serial port , Slave address 
 The host sends for score acquisition ：5a + 00 +  Read function code 03 +  Slave address  +  Check code  
 Return value ： fraction ( The data is correct );-1( The slave is not ready );-2( Data error )
******************************************************/
int get_score(serial &pipe, int addr){
	int check_code = 93 + addr, ret;				// The check code is cumulative sum 
	vector<uchar> code = {0x5a, 0x00, 0x03};
	vector<uchar> rec;
	code.insert(code.begin()+3, (uchar)addr);			// Insert slave address 
	code.push_back((uchar)check_code);				// Insert the check code 
	//cout << format(data) << endl;				
	

	/*  Write and receive response packets  */
	pipe.myWrite(code);
	sleep(1);
	rec = pipe.myRead(5);
	if(rec[3] == 0x6f) ret = -1;					// Check for errors 
	else {
	    ret = (int)rec[3];						// Turn to numbers 
	    if(ret < 0 || ret > 100) ret =-2;				// Check whether the number is legal 
	}
	return ret;

}
/***************************************************** 
 Slave reset ：
 Parameters ：serial A serial port , Slave score 
 Master sends for slave reset ：5a +  Broadcast address 00 +  Reset function code 01 + 00 + Check byte 
******************************************************/
void reset(serial &pipe){
	vector<uchar> code = {0x5a, 0x00, 0x01,0x00,0x5b};
	//cout <<"reset:"<< format(code) << endl;				
	/*  Send packet  */
	for(int i=0;i<600;i++) {
	    pipe.myWrite(code);
	}
	return;	    
}
```

```c
//serial.h
#ifndef SERIAL_H
#define SERIAL_H

#include <cstring>
#include <vector>
#include <sys/termios.h>


class serial {
private:
    int board = -1, epfd = -1;
public:
    serial(const char *board_path, speed_t baud_rate);
    ~serial();
    std::vector<unsigned char> myRead(size_t n) const;
    void myWrite(const std::vector<unsigned char> &data) const;
};

#endif //SERIAL_H
```

```c
//serial.c
#include "serial.h"
#include <cerrno>
#include <cstdio>
#include <iostream>
#include <sys/epoll.h>
#include <sys/fcntl.h>
#include <sys/termios.h>
#include <sys/unistd.h>
#include <stdio.h>
#include <signal.h>
#define err_check(code) if ((code) < 0) {    \
    printf("Error: %s\n", strerror(errno));  \
    _exit(1);                                \
}
serial::serial(const char *board_path, speed_t baud_rate) {
    err_check(board = open(board_path, O_RDWR | O_NOCTTY ))

    termios attrs {};
    tcgetattr(board, &attrs);
    //  set baud rate 
    err_check(cfsetispeed(&attrs, baud_rate))
    err_check(cfsetospeed(&attrs, baud_rate))
    attrs.c_iflag &= ~( BRKINT | ICRNL | INPCK | ISTRIP | IXON | IXOFF );
    attrs.c_oflag &= ~( OPOST | ONLCR | OCRNL );
    attrs.c_lflag &= ~( ECHO | ICANON | IEXTEN | ISIG );
    attrs.c_cflag &= ~( CSIZE | PARENB );
    attrs.c_cflag |= CS8;
    attrs.c_cc[VMIN]  = 1;
    attrs.c_cc[VTIME] = 0; 
    //  Set terminal parameters , All changes take effect immediately 
    err_check(tcsetattr(board, TCSANOW, &attrs))
    //  Reopen the device file to apply the new terminal parameters 
    close(board);
    err_check(board = open(board_path, O_RDWR | O_NOCTTY)) 
    //  Create a new  epoll  example , And return a file descriptor for control 
    err_check(epfd = epoll_create(1))
    
    epoll_event event {
        .events = EPOLLIN | EPOLLET,  //  An event is triggered when the opposite end becomes readable 
        .data = {
            .fd = board
        }
    };
    //  Add this event to  epoll  In the listening list 
    err_check(epoll_ctl(epfd, EPOLL_CTL_ADD, board, &event))
}
serial::~serial() {
    (~board) && close(board);
    (~epfd) && close(epfd);
}
std::vector<unsigned char> serial::myRead(size_t n) const {
    size_t count = 0;
    std::vector<unsigned char> buffer(n);

    while (count < n) 
    {
        epoll_event event {};
        //  Wait for data from the opposite end of the serial port 
        epoll_wait(epfd, &event, 1, 5000);		//  Specify the timeout value , Avoid indefinite blocking waiting 
        //  Reading data , Then decide whether to continue reading according to the amount of data read 
        count += ::read(board, &buffer[count], n); 
    }
    //tcflush(board,TCIOFLUSH);
    return buffer;
}
void serial::myWrite(const std::vector<unsigned char> &data) const {
    size_t count = 0;
    //tcflush(board,TCOFLUSH);
    while (count < data.size()) {
        //  Write data to serial port 
        count += ::write(board, &data[count], data.size() - count);
}
}

Programming objectives ： Deepen the understanding through this case RS485 communication mode , The main controller of the upper computer communicates with all the lower computers .

Description of program operation effect ： adopt RS232/RS485 The converter will be multiple with 485 The MCU of the lower computer control program of the module is mounted on the bus . Use a single chip microcomputer as the upper computer , Download hex file , Another single-chip microcomputer is used as the lower computer , Download the lower computer program . After the MCU of the lower computer is powered on , The first two digits of the nixie tube display the slave number , The last three digits show the scoring results . First press the center button of the navigation button to enter the setting mode , The selected set decimal point of the nixie tube is lit ; Then by controlling the left and right directions of the navigation keys, the position selection of the nixie tube is realized , The up and down direction realizes the addition and subtraction of the numerical value on the nixie tube , Press the center button again to exit the setting mode . Then press KEY2、KEY3 Press the key to mark the completion of slave number and scoring setting , The first 1 Position and number 8 position LED The light is on ; Finally, by controlling the slave detection and multi machine scoring buttons of the master controller of the upper computer , Get the slave number and score set by the MCU , So as to realize the communication between the upper computer and the lower computer .

The test method

1. Through the DuPont line 51 SCM and RS232/RS485 Converter connection , Re pass USB turn RS232/RS485 Serial communication line and PC Machine connection , download hex file , And power on the MCU ;

2. If you directly use a single chip microcomputer as the host , The MCU needs to download the contact software in the upper computer program instead of the lower computer software ;

3. The initial phenomenon after downloading from the lower computer is ： The leftmost two nixie tubes show 00 Indicates the slave number , Far right 3 A digital tube display 000 Indicates the score ;

4. Press the center button of the navigation key to enter the setting mode , Press the center key again to exit the setting mode after setting the slave number and scoring , Then press the KEY1,KEY2, Flag setting is complete ;

5. Control the upper computer to detect the slave computer and obtain the number of the lower computer , And get its score , The data is displayed on the main controller of the upper computer , Finally, finish scoring , Single chip microcomputer LED The light goes out .

Experimental experience

RS232 The interface only allows connections on the bus 1 A transceiver , Single station capacity . and RS485 The interface on the bus is allowed to connect up to 128 A transceiver . That is, it has multi station capability , So that users can take advantage of a single RS485 The interface makes it easy to set up a network of devices .RS485 It belongs to half duplex communication , Data can be transmitted in both directions of a signal carrier , But it cannot be transmitted at the same time . The level conversion adopts differential circuit mode ,A、B The voltage difference between the two lines is greater than 0.2 Think it's logic “1”, Less than -0.2 Think it's logic “0”, Only one of the two sides of the communication is sending , When one party is receiving , Communication can be carried out normally .RS485 Widely used in industrial automation control 、 Video surveillance 、 Access control intercom, building alarm and other fields .

This experiment makes us understand RS485 and RS232 With more understanding , Understand how they work .