modbus rtu代码示例

对于modbus RTU通信协议的代码示例，我们可以以C语言为例，使用串口通信库来实现。

以下是一个简单的modbus RTU通信示例，其中包括了从机和主机的代码：

从机代码：

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

#define BAUDRATE B9600
#define DEVICE "/dev/ttyUSB0"
#define SLAVEADDR 1

int main(int argc, char **argv) {
    int fd, n;
    struct termios oldtio, newtio;
    unsigned char buf[256];
    unsigned char response[256];

    fd = open(DEVICE, O_RDWR | O_NOCTTY);
    if (fd < 0) {
        perror(DEVICE);
        exit(-1);
    }

    tcgetattr(fd, &oldtio);
    bzero(&newtio, sizeof(newtio));
    newtio.c_cflag = BAUDRATE | CS8 | CLOCAL | CREAD;
    newtio.c_iflag = IGNPAR | ICRNL;
    newtio.c_oflag = 0;
    newtio.c_lflag = ICANON;
    tcflush(fd, TCIFLUSH);
    tcsetattr(fd,TCSANOW,&newtio);

    while (1) {
        bzero(buf, sizeof(buf));
        n = read(fd, buf, sizeof(buf));
        if (n > 0 && buf[0] == SLAVEADDR && buf[1] == 0x03) {
            int addr = (buf[2] << 8) | buf[3];
            int count = (buf[4] << 8) | buf[5];
            bzero(response, sizeof(response));
            response[0] = SLAVEADDR;
            response[1] = 0x03;
            response[2] = count * 2;
            for (int i = 0; i < count; i++) {
                int value = i + addr;
                response[3 + i * 2] = (value >> 8) & 0xff;
                response[4 + i * 2] = value & 0xff;
            }
            write(fd, response, 3 + count * 2);
        }
    }

    tcsetattr(fd,TCSANOW,&oldtio);
    close(fd);
    return 0;
}

主机代码：

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

#define BAUDRATE B9600
#define DEVICE "/dev/ttyUSB0"
#define SLAVEADDR 1

int main(int argc, char **argv) {
    int fd, n;
    struct termios oldtio, newtio;
    unsigned char buf[256];
    unsigned char request[256];

    fd = open(DEVICE, O_RDWR | O_NOCTTY);
    if (fd < 0) {
        perror(DEVICE);
        exit(-1);
    }

    tcgetattr(fd, &oldtio);
    bzero(&newtio, sizeof(newtio));
    newtio.c_cflag = BAUDRATE | CS8 | CLOCAL | CREAD;
    newtio.c_iflag = IGNPAR | ICRNL;
    newtio.c_oflag = 0;
    newtio.c_lflag = ICANON;
    tcflush(fd, TCIFLUSH);
    tcsetattr(fd,TCSANOW,&newtio);

    int startAddr = 0;
    int count = 10;
    bzero(request, sizeof(request));
    request[0] = SLAVEADDR;
    request[1] = 0x03;
    request[2] = (startAddr >> 8) & 0xff;
    request[3] = startAddr & 0xff;
    request[4] = (count >> 8) & 0xff;
    request[5] = count & 0xff;
    int crc = 0xFFFF;
    for (int i = 0; i < 6; i++) {
        crc ^= request[i];
        for (int j = 0; j < 8; j++) {
            if (crc & 0x0001) {
                crc >>= 1;
                crc ^= 0xA001;
            } else {
                crc >>= 1;
            }
        }
    }
    request[6] = crc & 0xff;
    request[7] = (crc >> 8) & 0xff;
    write(fd, request, 8);

    bzero(buf, sizeof(buf));
    n = read(fd, buf, sizeof(buf));
    if (n > 0 && buf[0] == SLAVEADDR && buf[1] == 0x03) {
        int count = buf[2] / 2;
        for (int i = 0; i < count; i++) {
            int value = (buf[3 + i * 2] << 8) | buf[4 + i * 2];
            printf("Address: %d, Value: %d\n", startAddr + i, value);
        }
    }

    tcsetattr(fd,TCSANOW,&oldtio);
    close(fd);
    return 0;
}

在这个示例中，从机接收主机的读请求，并返回对应地址的数据。主机发送读请求，并解析从机返回的数据。示例中使用了一个简单的CRC16校验，不过实际使用中还需要根据协议的要求进行校验。