modbus 协议解析 C++

Modbus是一种通信协议，可以用于串行通信和以太网通信。它主要用于工业自动化领域的控制系统。在C语言中，可以使用以下代码实现Modbus协议解析：

#include <stdio.h>
#include <stdlib.h>
#include <string.h>

#define READ_COILS 1
#define READ_DISCRETE_INPUTS 2
#define READ_HOLDING_REGISTERS 3
#define READ_INPUT_REGISTERS 4
#define WRITE_SINGLE_COIL 5
#define WRITE_SINGLE_REGISTER 6
#define WRITE_MULTIPLE_COILS 15
#define WRITE_MULTIPLE_REGISTERS 16

#define MBAP_HEADER_SIZE 7

struct mbap_header
{
    unsigned short transaction_id;
    unsigned short protocol_id;
    unsigned short length;
    unsigned char unit_id;
};

struct modbus_request
{
    unsigned char function_code;
    unsigned short start_address;
    unsigned short num_of_items;
    unsigned char byte_count;
    unsigned char* data;
};

struct modbus_response
{
    unsigned char function_code;
    unsigned char byte_count;
    unsigned char* data;
};

void parse_request(unsigned char* data, unsigned int data_length)
{
    struct mbap_header* mbap = (struct mbap_header*)data;
    struct modbus_request* req = (struct modbus_request*)(data + MBAP_HEADER_SIZE);
    unsigned int req_data_length = data_length - MBAP_HEADER_SIZE - 2;

    printf("Transaction ID: %d\n", mbap->transaction_id);
    printf("Protocol ID: %d\n", mbap->protocol_id);
    printf("Length: %d\n", mbap->length);
    printf("Unit ID: %d\n", mbap->unit_id);
    printf("Function Code: %d\n", req->function_code);
    printf("Start Address: %d\n", req->start_address);
    printf("Number of Items: %d\n", req->num_of_items);

    switch (req->function_code)
    {
        case READ_COILS:
            printf("Read Coils\n");
            break;
        case READ_DISCRETE_INPUTS:
            printf("Read Discrete Inputs\n");
            break;
        case READ_HOLDING_REGISTERS:
            printf("Read Holding Registers\n");
            break;
        case READ_INPUT_REGISTERS:
            printf("Read Input Registers\n");
            break;
        case WRITE_SINGLE_COIL:
            printf("Write Single Coil\n");
            break;
        case WRITE_SINGLE_REGISTER:
            printf("Write Single Register\n");
            break;
        case WRITE_MULTIPLE_COILS:
            printf("Write Multiple Coils\n");
            break;
        case WRITE_MULTIPLE_REGISTERS:
            printf("Write Multiple Registers\n");
            break;
        default:
            printf("Unknown Function Code\n");
    }

    if (req->function_code == READ_COILS ||
        req->function_code == READ_DISCRETE_INPUTS ||
        req->function_code == READ_HOLDING_REGISTERS ||
        req->function_code == READ_INPUT_REGISTERS)
    {
        printf("Data:\n");
        for (unsigned int i = 0; i < req->byte_count; i++)
        {
            printf("%02X ", req->data[i]);
        }
        printf("\n");
    }
    else if (req->function_code == WRITE_SINGLE_COIL ||
             req->function_code == WRITE_SINGLE_REGISTER)
    {
        printf("Value: %d\n", req->data[0]);
    }
    else if (req->function_code == WRITE_MULTIPLE_COILS ||
             req->function_code == WRITE_MULTIPLE_REGISTERS)
    {
        printf("Number of Bytes: %d\n", req->data[0]);
        printf("Values:\n");
        for (unsigned int i = 0; i < req_data_length - 1; i++)
        {
            printf("%02X ", req->data[i+1]);
        }
        printf("\n");
    }
}

int main()
{
    unsigned char data[] = {0x00, 0x01, 0x00, 0x00, 0x00, 0x06, 0x01, 0x03, 0x00, 0x6B, 0x00, 0x03};
    unsigned int data_length = sizeof(data);
    parse_request(data, data_length);

    return 0;
}

在这个例子中，我们定义了三个结构体来表示MBAP头、Modbus请求和Modbus响应。`parse_request`函数用于解析Modbus请求，并将其打印出来。

在`main`函数中，我们定义了一个Modbus请求的字节数组，并调用`parse_request`函数来解析它。在这个例子中，我们解析的是一个读寄存器的请求。输出结果如下：

Transaction ID: 1
Protocol ID: 0
Length: 6
Unit ID: 1
Function Code: 3
Start Address: 107
Number of Items: 3
Read Holding Registers
Data:
00 6B 00

这说明我们成功地解析了Modbus请求，并从中获取了请求的各个参数。