c语言modbus协议源码

以下是一个简单的C语言modbus协议源码，可以实现modbus RTU通信：

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

#define MODBUS_RTU_SLAVEID              0x01
#define MODBUS_RTU_FUNCTION_READ        0x03
#define MODBUS_RTU_FUNCTION_WRITE       0x06
#define MODBUS_RTU_FUNCTION_WRITEMULTI  0x10
#define MODBUS_RTU_CRC_POLYNOMIAL       0xA001

unsigned short modbus_crc16(unsigned char *buf, int len)
{
    unsigned short crc = 0xFFFF;
    int i, j;

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

    return crc;
}

int modbus_send(int fd, unsigned char *buf, int len)
{
    int n;

    n = write(fd, buf, len);
    if (n != len) {
        return -1;
    }

    return 0;
}

int modbus_recv(int fd, unsigned char *buf, int len, int timeout)
{
    int n, count = 0;

    while (count < timeout) {
        n = read(fd, buf, len);
        if (n > 0) {
            return n;
        }
        count++;
        usleep(1000);
    }

    return -1;
}

int modbus_read(int fd, unsigned char *buf, int addr, int count)
{
    unsigned char frame[8], resp[255];
    int i, len;

    frame[0] = MODBUS_RTU_SLAVEID;
    frame[1] = MODBUS_RTU_FUNCTION_READ;
    frame[2] = (addr >> 8) & 0xFF;
    frame[3] = addr & 0xFF;
    frame[4] = (count >> 8) & 0xFF;
    frame[5] = count & 0xFF;

    len = 6;
    *(unsigned short *)(frame + len) = modbus_crc16(frame, len);
    len += 2;

    if (modbus_send(fd, frame, len) < 0) {
        return -1;
    }

    len = modbus_recv(fd, resp, 255, 100);
    if (len < 0) {
        return -1;
    }

    if (len < 5) {
        return -1;
    }

    if (resp[0] != MODBUS_RTU_SLAVEID) {
        return -1;
    }

    if (resp[1] != MODBUS_RTU_FUNCTION_READ) {
        return -1;
    }

    if (resp[2] != count * 2) {
        return -1;
    }

    for (i = 0; i < count; i++) {
        buf[i * 2] = resp[3 + i * 2];
        buf[i * 2 + 1] = resp[4 + i * 2];
    }

    return count;
}

int modbus_write(int fd, unsigned char *buf, int addr, int value)
{
    unsigned char frame[8], resp[8];
    int len;

    frame[0] = MODBUS_RTU_SLAVEID;
    frame[1] = MODBUS_RTU_FUNCTION_WRITE;
    frame[2] = (addr >> 8) & 0xFF;
    frame[3] = addr & 0xFF;
    frame[4] = (value >> 8) & 0xFF;
    frame[5] = value & 0xFF;

    len = 6;
    *(unsigned short *)(frame + len) = modbus_crc16(frame, len);
    len += 2;

    if (modbus_send(fd, frame, len) < 0) {
        return -1;
    }

    len = modbus_recv(fd, resp, 8, 100);
    if (len < 0) {
        return -1;
    }

    if (len < 5) {
        return -1;
    }

    if (resp[0] != MODBUS_RTU_SLAVEID) {
        return -1;
    }

    if (resp[1] != MODBUS_RTU_FUNCTION_WRITE) {
        return -1;
    }

    if (resp[2] != (addr >> 8) & 0xFF || resp[3] != addr & 0xFF) {
        return -1;
    }

    if (*(unsigned short *)(resp + 4) != *(unsigned short *)(frame + 4)) {
        return -1;
    }

    return 0;
}

int modbus_writemulti(int fd, unsigned char *buf, int addr, int count, unsigned short *values)
{
    unsigned char frame[255], resp[8];
    int i, len;

    frame[0] = MODBUS_RTU_SLAVEID;
    frame[1] = MODBUS_RTU_FUNCTION_WRITEMULTI;
    frame[2] = (addr >> 8) & 0xFF;
    frame[3] = addr & 0xFF;
    frame[4] = (count >> 8) & 0xFF;
    frame[5] = count & 0xFF;
    frame[6] = count * 2;

    for (i = 0; i < count; i++) {
        frame[7 + i * 2] = (values[i] >> 8) & 0xFF;
        frame[8 + i * 2] = values[i] & 0xFF;
    }

    len = 7 + count * 2;
    *(unsigned short *)(frame + len) = modbus_crc16(frame, len);
    len += 2;

    if (modbus_send(fd, frame, len) < 0) {
        return -1;
    }

    len = modbus_recv(fd, resp, 8, 100);
    if (len < 0) {
        return -1;
    }

    if (len < 5) {
        return -1;
    }

    if (resp[0] != MODBUS_RTU_SLAVEID) {
        return -1;
    }

    if (resp[1] != MODBUS_RTU_FUNCTION_WRITEMULTI) {
        return -1;
    }

    if (resp[2] != (addr >> 8) & 0xFF || resp[3] != addr & 0xFF) {
        return -1;
    }

    if (*(unsigned short *)(resp + 4) != *(unsigned short *)(frame + 4)) {
        return -1;
    }

    return 0;
}

int main()
{
    int fd, ret, i;
    unsigned char buf[256];
    unsigned short values[16];

    fd = open("/dev/ttyS0", O_RDWR);
    if (fd < 0) {
        printf("open error\n");
        return -1;
    }

    struct termios options;
    tcgetattr(fd, &options);
    options.c_cflag |= B9600;
    options.c_cflag &= ~PARENB;
    options.c_cflag &= ~CSTOPB;
    options.c_cflag &= ~CSIZE;
    options.c_cflag |= CS8;
    options.c_cc[VMIN] = 1;
    options.c_cc[VTIME] = 0;
    tcsetattr(fd, TCSANOW, &options);

    ret = modbus_read(fd, buf, 0x1000, 16);
    if (ret < 0) {
        printf("read error\n");
        return -1;
    }

    for (i = 0; i < ret; i++) {
        values[i] = (buf[i * 2] << 8) | buf[i * 2 + 1];
    }

    values[0]++;

    ret = modbus_write(fd, buf, 0x1000, values[0]);
    if (ret < 0) {
        printf("write error\n");
        return -1;
    }

    for (i = 0; i < 16; i++) {
        values[i] += i;
    }

    ret = modbus_writemulti(fd, buf, 0x1010, 16, values);
    if (ret < 0) {
        printf("write multi error\n");
        return -1;
    }

    printf("success\n");

    close(fd);

    return 0;
}

该源码通过串口通信实现modbus RTU协议的读写操作，其中包括modbus CRC16校验的计算和使用。可以根据实际需求进行修改和扩展。