c++ modbus RTU代码

下面是一个基于C++的Modbus RTU通信代码示例：

#include <iostream>
#include <cstring>
#include <cerrno>
#include <cstdlib>
#include <cstdio>
#include <unistd.h>
#include <fcntl.h>
#include <termios.h>

using namespace std;

int open_port(const char* port) {
    int fd = open(port, O_RDWR | O_NOCTTY | O_NDELAY);
    if (fd == -1) {
        perror("open_port: Unable to open serial port");
    } else {
        fcntl(fd, F_SETFL, 0);
    }
    return (fd);
}

int set_port(int fd, int baud_rate, int data_bits, int stop_bits, char parity) {
    struct termios options;
    if (tcgetattr(fd, &options) == -1) {
        perror("set_port: Unable to get port settings");
        return (-1);
    }
    cfsetispeed(&options, baud_rate);
    cfsetospeed(&options, baud_rate);
    options.c_cflag |= (CLOCAL | CREAD);
    options.c_cflag &= ~CSIZE;
    switch (data_bits) {
    case 5:
        options.c_cflag |= CS5;
        break;
    case 6:
        options.c_cflag |= CS6;
        break;
    case 7:
        options.c_cflag |= CS7;
        break;
    case 8:
        options.c_cflag |= CS8;
        break;
    default:
        fprintf(stderr, "Unsupported data size\n");
        return (-1);
    }
    switch (parity) {
    case 'n':
    case 'N':
        options.c_cflag &= ~PARENB;
        options.c_iflag &= ~INPCK;
        break;
    case 'o':
    case 'O':
        options.c_cflag |= (PARODD | PARENB);
        options.c_iflag |= INPCK;
        break;
    case 'e':
    case 'E':
        options.c_cflag |= PARENB;
        options.c_cflag &= ~PARODD;
        options.c_iflag |= INPCK;
        break;
    default:
        fprintf(stderr, "Unsupported parity\n");
        return (-1);
    }
    switch (stop_bits) {
    case 1:
        options.c_cflag &= ~CSTOPB;
        break;
    case 2:
        options.c_cflag |= CSTOPB;
        break;
    default:
        fprintf(stderr, "Unsupported stop bits\n");
        return (-1);
    }
    options.c_cc[VTIME] = 0;
    options.c_cc[VMIN] = 1;
    tcflush(fd, TCIFLUSH);
    if (tcsetattr(fd, TCSANOW, &options) == -1) {
        perror("set_port: Unable to set port settings");
        return (-1);
    }
    return (0);
}

int modbus_read_registers(int fd, unsigned char slave_addr, unsigned short start_addr, unsigned short count, unsigned short* values) {
    unsigned char buf[256];
    int i, len;
    buf[0] = slave_addr;
    buf[1] = 0x03;
    buf[2] = start_addr >> 8;
    buf[3] = start_addr & 0xff;
    buf[4] = count >> 8;
    buf[5] = count & 0xff;
    len = 6;
    unsigned short crc = 0xFFFF;
    for (i = 0; i < len; i++) {
        crc ^= buf[i];
        for (int j = 0; j < 8; j++) {
            if (crc & 1) {
                crc >>= 1;
                crc ^= 0xA001;
            } else {
                crc >>= 1;
            }
        }
    }
    buf[len++] = crc & 0xff;
    buf[len++] = crc >> 8;
    int n = write(fd, buf, len);
    if (n != len) {
        perror("modbus_read_registers: Unable to write to port");
        return (-1);
    }
    usleep(10000);
    len = read(fd, buf, 256);
    if (len < 5) {
        perror("modbus_read_registers: Error reading from port");
        return (-1);
    }
    crc = 0xFFFF;
    for (i = 0; i < len - 2; i++) {
        crc ^= buf[i];
        for (int j = 0; j < 8; j++) {
            if (crc & 1) {
                crc >>= 1;
                crc ^= 0xA001;
            } else {
                crc >>= 1;
            }
        }
    }
    if (crc != (buf[len - 2] | (buf[len - 1] << 8))) {
        perror("modbus_read_registers: CRC error");
        return (-1);
    }
    if (buf[1] & 0x80) {
        perror("modbus_read_registers: Exception response");
        return (-1);
    }
    for (i = 0; i < count; i++) {
        values[i] = buf[3 + i * 2] << 8 | buf[4 + i * 2];
    }
    return (0);
}

int main() {
    const char* port = "/dev/ttyUSB0";
    int baud_rate = B9600;
    int data_bits = 8;
    int stop_bits = 1;
    char parity = 'N';
    int fd = open_port(port);
    if (fd == -1) {
        return (EXIT_FAILURE);
    }
    if (set_port(fd, baud_rate, data_bits, stop_bits, parity) == -1) {
        return (EXIT_FAILURE);
    }
    unsigned short values[256];
    if (modbus_read_registers(fd, 1, 0, 10, values) == -1) {
        return (EXIT_FAILURE);
    }
    for (int i = 0; i < 10; i++) {
        cout << values[i] << endl;
    }
    close(fd);
    return (EXIT_SUCCESS);
}

这个代码示例使用Linux系统提供的串口设备文件进行通信，并且实现了读取Modbus RTU从设备的寄存器的功能。需要注意的是，Modbus RTU通信需要进行CRC校验，这个代码示例中使用了一个CRC计算函数来实现校验。在实际使用中，你需要根据自己的具体需求进行修改。