c语言modbus-rtu的代码

下面是一个简单的C语言Modbus RTU通信的示例代码：

#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <unistd.h>
#include <errno.h>
#include <termios.h>
#include <fcntl.h>

#define SLAVE_ADDR 0x01
#define FUNCTION_CODE_READ_HOLDING_REGISTERS 0x03
#define FUNCTION_CODE_WRITE_SINGLE_REGISTER 0x06

int open_serial_port(const char *port_name) {
    int fd = open(port_name, O_RDWR | O_NOCTTY | O_NDELAY);
    if (fd == -1) {
        printf("Failed to open serial port %s: %s\n", port_name, strerror(errno));
    } else {
        struct termios options;
        tcgetattr(fd, &options);

        // Set baud rate
        cfsetispeed(&options, B9600);
        cfsetospeed(&options, B9600);

        // Set data bits, parity, and stop bits
        options.c_cflag &= ~CSIZE;
        options.c_cflag |= CS8;
        options.c_cflag &= ~PARENB;
        options.c_cflag &= ~CSTOPB;

        // Enable receiver and ignore modem control lines
        options.c_cflag |= CREAD | CLOCAL;

        // Disable software flow control
        options.c_iflag &= ~(IXON | IXOFF | IXANY);

        // Set the new options for the port
        tcsetattr(fd, TCSANOW, &options);
    }
    return fd;
}

void close_serial_port(int fd) {
    close(fd);
}

unsigned short crc16(unsigned char *buf, int len) {
    unsigned short crc = 0xFFFF;
    for (int pos = 0; pos < len; pos++) {
        crc ^= (unsigned short)buf[pos];
        for (int i = 8; i != 0; i--) {
            if ((crc & 0x0001) != 0) {
                crc >>= 1;
                crc ^= 0xA001;
            } else {
                crc >>= 1;
            }
        }
    }
    return crc;
}

int send_request(int fd, unsigned char *buf, int len) {
    unsigned short crc = crc16(buf, len);
    buf[len++] = crc & 0xFF;
    buf[len++] = (crc >> 8) & 0xFF;
    return write(fd, buf, len);
}

int receive_response(int fd, unsigned char *buf) {
    int len = 0;
    while (len < 3 || len < (buf[2] + 5)) {
        int n = read(fd, &buf[len], 256);
        if (n <= 0) {
            return -1;
        }
        len += n;
    }
    if (buf[1] & 0x80) {
        printf("Modbus exception %d\n", buf[2]);
        return -1;
    }
    return len;
}

int read_holding_registers(int fd, unsigned short register_address, unsigned short num_registers, unsigned short *data) {
    unsigned char buf[256];
    int len = 0;

    // Request
    buf[len++] = SLAVE_ADDR;
    buf[len++] = FUNCTION_CODE_READ_HOLDING_REGISTERS;
    buf[len++] = (register_address >> 8) & 0xFF;
    buf[len++] = register_address & 0xFF;
    buf[len++] = (num_registers >> 8) & 0xFF;
    buf[len++] = num_registers & 0xFF;
    if (send_request(fd, buf, len) == -1) {
        printf("Failed to send request: %s\n", strerror(errno));
        return -1;
    }

    // Response
    if (receive_response(fd, buf) == -1) {
        printf("Failed to receive response: %s\n", strerror(errno));
        return -1;
    }
    if (buf[2] != num_registers * 2) {
        printf("Invalid response length\n");
        return -1;
    }
    for (int i = 0; i < num_registers; i++) {
        data[i] = (buf[3 + i * 2] << 8) | buf[4 + i * 2];
    }
    return 0;
}

int write_single_register(int fd, unsigned short register_address, unsigned short value) {
    unsigned char buf[256];
    int len = 0;

    // Request
    buf[len++] = SLAVE_ADDR;
    buf[len++] = FUNCTION_CODE_WRITE_SINGLE_REGISTER;
    buf[len++] = (register_address >> 8) & 0xFF;
    buf[len++] = register_address & 0xFF;
    buf[len++] = (value >> 8) & 0xFF;
    buf[len++] = value & 0xFF;
    if (send_request(fd, buf, len) == -1) {
        printf("Failed to send request: %s\n", strerror(errno));
        return -1;
    }

    // Response
    if (receive_response(fd, buf) == -1) {
        printf("Failed to receive response: %s\n", strerror(errno));
        return -1;
    }
    if (buf[2] != value >> 8 || buf[3] != value & 0xFF) {
        printf("Invalid response\n");
        return -1;
    }
    return 0;
}

int main(int argc, char **argv) {
    int fd = open_serial_port("/dev/ttyUSB0");
    if (fd == -1) {
        return -1;
    }

    unsigned short data[16];
    if (read_holding_registers(fd, 0x0000, 16, data) == -1) {
        close_serial_port(fd);
        return -1;
    }
    for (int i = 0; i < 16; i++) {
        printf("Register %d: %d\n", i, data[i]);
    }

    if (write_single_register(fd, 0x0000, 12345) == -1) {
        close_serial_port(fd);
        return -1;
    }

    close_serial_port(fd);
    return 0;
}

这个示例代码包含了以下功能：

- 打开串口
- 发送读保持寄存器的请求并接收响应
- 发送写单个寄存器的请求并接收响应
- 计算CRC16校验和

你可以根据自己的需求修改代码。注意，该示例代码仅供参考，实际使用时需要根据具体情况进行修改和测试。