modbus rtu c语言代码实现

以下是一个简单的 Modbus RTU 的 C 语言代码示例，用于读取一个保持寄存器：

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

#define SLAVE_ADDRESS 1
#define FUNCTION_CODE 0x03
#define START_ADDRESS 0x0000
#define NUM_REGISTERS 0x0001

#define RESPONSE_SIZE 5
#define MAX_BUFFER_SIZE 256

unsigned short crc16(unsigned char *buf, unsigned int len)
{
    unsigned short crc = 0xFFFF;
    unsigned int i, j;

    for (i = 0; i < len; i++) {
        crc ^= buf[i];
        for (j = 0; j < 8; j++) {
            if (crc & 0x0001) {
                crc >>= 1;
                crc ^= 0xA001;
            } else {
                crc >>= 1;
            }
        }
    }

    return crc;
}

int main(int argc, char *argv[])
{
    int fd;
    struct termios options;
    unsigned char buffer[MAX_BUFFER_SIZE] = {0};
    unsigned int buffer_len = 0;
    unsigned short crc = 0;
    unsigned char response[RESPONSE_SIZE] = {0};
    int num_bytes_read = 0;

    // Open the serial port
    fd = open("/dev/ttyS0", O_RDWR | O_NOCTTY | O_NDELAY);
    if (fd == -1) {
        perror("open");
        return -1;
    }

    // Configure the serial port
    tcgetattr(fd, &options);
    cfsetispeed(&options, B9600);
    cfsetospeed(&options, B9600);
    options.c_cflag &= ~PARENB;
    options.c_cflag &= ~CSTOPB;
    options.c_cflag &= ~CSIZE;
    options.c_cflag |= CS8;
    options.c_cflag &= ~CRTSCTS;
    options.c_cflag |= CREAD | CLOCAL;
    options.c_iflag &= ~(IXON | IXOFF | IXANY);
    options.c_lflag &= ~(ICANON | ECHO | ECHOE | ISIG);
    options.c_oflag &= ~OPOST;
    options.c_cc[VMIN] = 0;
    options.c_cc[VTIME] = 10;
    tcsetattr(fd, TCSANOW, &options);

    // Build the request packet
    buffer[0] = SLAVE_ADDRESS;
    buffer[1] = FUNCTION_CODE;
    buffer[2] = START_ADDRESS >> 8;
    buffer[3] = START_ADDRESS & 0xFF;
    buffer[4] = NUM_REGISTERS >> 8;
    buffer[5] = NUM_REGISTERS & 0xFF;
    crc = crc16(buffer, 6);
    buffer[6] = crc & 0xFF;
    buffer[7] = crc >> 8;
    buffer_len = 8;

    // Send the request packet
    write(fd, buffer, buffer_len);

    // Wait for the response packet
    num_bytes_read = read(fd, response, RESPONSE_SIZE);
    if (num_bytes_read < RESPONSE_SIZE) {
        printf("Error: response packet too short\n");
        close(fd);
        return -1;
    }

    // Verify the response packet
    crc = crc16(response, RESPONSE_SIZE - 2);
    if (crc != (response[RESPONSE_SIZE - 1] << 8 | response[RESPONSE_SIZE - 2])) {
        printf("Error: response packet CRC check failed\n");
        close(fd);
        return -1;
    }

    // Print the register value
    printf("Register value: %u\n", (response[3] << 8) | response[4]);

    // Close the serial port
    close(fd);

    return 0;
}

请注意，此示例仅用于演示目的，并且可能需要进行修改以适应您的特定应用程序。还请注意，此示例仅处理单个保持寄存器读取请求，您可能需要自己实现其他 Modbus RTU 功能码的支持。