工控机和51单片机485通信C++实现代码示例

以下是一个简单的 C++ 示例代码，演示如何在工控机和 51 单片机之间通过 485 总线进行通信。

工控机端代码：

#include <iostream>
#include <Windows.h>

using namespace std;

int main()
{
    HANDLE hCom = CreateFile("COM1", GENERIC_READ | GENERIC_WRITE, 0, NULL, OPEN_EXISTING, 0, NULL);
    if (hCom == INVALID_HANDLE_VALUE) {
        cerr << "Failed to open COM1 port" << endl;
        return 1;
    }

    DCB dcb;
    dcb.DCBlength = sizeof(dcb);
    GetCommState(hCom, &dcb);
    dcb.BaudRate = CBR_9600;
    dcb.ByteSize = 8;
    dcb.Parity = NOPARITY;
    dcb.StopBits = ONESTOPBIT;
    SetCommState(hCom, &dcb);

    char txData[] = { 0x01, 0x03, 0x00, 0x00, 0x00, 0x02, 0xc4, 0x0b };
    DWORD bytesWritten;
    WriteFile(hCom, txData, sizeof(txData), &bytesWritten, NULL);

    char rxData[256];
    DWORD bytesRead;
    ReadFile(hCom, rxData, sizeof(rxData), &bytesRead, NULL);

    for (int i = 0; i < bytesRead; i++) {
        printf("%02X ", rxData[i]);
    }
    putchar('\n');

    CloseHandle(hCom);

    return 0;
}

51 单片机端代码：

#include <reg52.h>

sbit RS485_EN = P2^0;

void initRS485()
{
    SCON = 0x50;    // 8-bit UART, no parity, 1 stop bit
    TMOD &= 0x0F;   // T1 in 8-bit auto-reload mode
    TMOD |= 0x20;
    TH1 = 0xFD;     // 9600 baud rate
    TL1 = 0xFD;
    TR1 = 1;        // enable timer1

    RS485_EN = 0;   // set RE/DE to receive
}

void sendByte(unsigned char byte)
{
    SBUF = byte;
    while (!TI);    // wait until byte is sent
    TI = 0;         // clear the flag
}

unsigned char recvByte()
{
    while (!RI);    // wait until byte is received
    RI = 0;         // clear the flag
    return SBUF;
}

void main()
{
    initRS485();

    while (1) {
        unsigned char rxData[256];
        unsigned char rxLen = 0;

        while (1) {
            // wait for the start byte
            while (recvByte() != 0x01);

            // check the function code
            if (recvByte() != 0x03) {
                continue;
            }

            // read the data length
            unsigned char len = recvByte();

            // read the data
            for (unsigned char i = 0; i < len; i++) {
                rxData[i] = recvByte();
            }
            rxLen = len;

            // calculate the CRC
            unsigned short crc = 0xFFFF;
            for (unsigned char i = 0; i < len + 2; i++) {
                crc ^= recvByte();
                for (unsigned char j = 0; j < 8; j++) {
                    if (crc & 0x0001) {
                        crc = (crc >> 1) ^ 0xA001;
                    } else {
                        crc = crc >> 1;
                    }
                }
            }
            if (crc == 0) {
                break;
            }
        }

        // send the response
        unsigned char txData[] = { 0x01, 0x03, rxLen, 0x00, 0x01, 0x02, 0x34, 0x12 };
        for (unsigned char i = 0; i < sizeof(txData) - 2; i++) {
            sendByte(txData[i]);
        }
        // append the CRC
        unsigned short crc = 0xFFFF;
        for (unsigned char i = 0; i < sizeof(txData) - 2; i++) {
            crc ^= txData[i];
            for (unsigned char j = 0; j < 8; j++) {
                if (crc & 0x0001) {
                    crc = (crc >> 1) ^ 0xA001;
                } else {
                    crc = crc >> 1;
                }
            }
        }
        sendByte(crc & 0xFF);
        sendByte(crc >> 8);

        // enable receiver
        RS485_EN = 0;
    }
}

注意：这只是一个简单的示例代码，实际应用可能需要根据具体情况进行修改。