Example code for implementing Modbus TCP communication based on C language embedded system

#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <errno.h>
#include <unistd.h>
#include <fcntl.h>
#include <termios.h>
#include <sys/socket.h>
#include <netinet/in.h>
#include <arpa/inet.h>

#define PORT 502

#define SERVER_IP "192.168.0.100"
#define DEVICE_ID 1

#define BUFFER_SIZE 1024

int main() {
    // 创建TCP连接
    int sockfd;
    struct sockaddr_in server_addr;

    sockfd = socket(AF_INET, SOCK_STREAM, 0);
    if (sockfd == -1) {
        printf("Failed to create socket: %sn", strerror(errno));
        return 1;
    }

    server_addr.sin_family = AF_INET;
    server_addr.sin_port = htons(PORT);
    server_addr.sin_addr.s_addr = inet_addr(SERVER_IP);

    if (connect(sockfd, (struct sockaddr *)&server_addr, sizeof(server_addr)) == -1) {
        printf("Failed to connect to server: %sn", strerror(errno));
        close(sockfd);
        return 1;
    }

    printf("Connected to server successfully.n");

    // 准备modbus请求
    unsigned char request[BUFFER_SIZE];
    unsigned char response[BUFFER_SIZE];
    int request_length, response_length;

    // 读保持寄存器
    int register_address = 0;
    int register_count = 4;
    request_length = modbus_build_request(request, DEVICE_ID, MODBUS_FC_READ_HOLDING_REGISTERS, register_address, register_count);

    // 发送modbus请求
    if (send(sockfd, request, request_length, 0) == -1) {
        printf("Failed to send request: %sn", strerror(errno));
        close(sockfd);
        return 1;
    }

    printf("Sent request successfully.n");

    // 接收modbus响应
    response_length = recv(sockfd, response, BUFFER_SIZE, 0);
    if (response_length == -1) {
        printf("Failed to receive response: %sn", strerror(errno));
        close(sockfd);
        return 1;
    }

    printf("Received response successfully.n");

    // 解析modbus响应
    int register_value = modbus_get_response_value(response, response_length);

    printf("Register value: %dn", register_value);

    // 关闭TCP连接
    close(sockfd);

    return 0;
}

#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <errno.h>
#include <unistd.h>
#include <fcntl.h>
#include <termios.h>
#include <sys/socket.h>
#include <netinet/in.h>
#include <arpa/inet.h>

#define PORT 502

#define SERVER_IP "192.168.0.100"
#define DEVICE_ID 1

#define BUFFER_SIZE 1024

int main() {
    // 创建TCP连接
    int sockfd;
    struct sockaddr_in server_addr;

    sockfd = socket(AF_INET, SOCK_STREAM, 0);
    if (sockfd == -1) {
        printf("Failed to create socket: %sn", strerror(errno));
        return 1;
    }

    server_addr.sin_family = AF_INET;
    server_addr.sin_port = htons(PORT);
    server_addr.sin_addr.s_addr = inet_addr(SERVER_IP);

    if (connect(sockfd, (struct sockaddr *)&server_addr, sizeof(server_addr)) == -1) {
        printf("Failed to connect to server: %sn", strerror(errno));
        close(sockfd);
        return 1;
    }

    printf("Connected to server successfully.n");

    // 准备modbus请求
    unsigned char request[BUFFER_SIZE];
    unsigned char response[BUFFER_SIZE];
    int request_length, response_length;

    // 读保持寄存器
    int register_address = 0;
    int register_count = 4;
    request_length = modbus_build_request(request, DEVICE_ID, MODBUS_FC_READ_HOLDING_REGISTERS, register_address, register_count);

    // 发送modbus请求
    if (send(sockfd, request, request_length, 0) == -1) {
        printf("Failed to send request: %sn", strerror(errno));
        close(sockfd);
        return 1;
    }

    printf("Sent request successfully.n");

    // 接收modbus响应
    response_length = recv(sockfd, response, BUFFER_SIZE, 0);
    if (response_length == -1) {
        printf("Failed to receive response: %sn", strerror(errno));
        close(sockfd);
        return 1;
    }

    printf("Received response successfully.n");

    // 解析modbus响应
    int register_value = modbus_get_response_value(response, response_length);

    printf("Register value: %dn", register_value);

    // 关闭TCP连接
    close(sockfd);

    return 0;
}