[MFC development] serial port communication example

I just learned a little bit about serial port recently , Specific about “ A serial port ”、“USB”、“HID” And other related words , You can go to Baidu by yourself , Or read a book .

Here I will share a simple operation , stay MFC in , Use the program to realize the communication between the upper computer and the lower computer . What about the upper computer , This is the computer , What about the next computer , I choose a treasure that I can buy USB Relay . If you don't know what the relay is, you can baidu , I won't go into details either .

This USB What about the relay , It can be used as in the red circle “A0 01 01 A2” To achieve communication , This is 16 It's binary .

If you have a serial port debugging assistant , You can open it , hold USB Plug the relay into the computer , Then follow the operation on the following figure , You will hear “ Crack ” A voice , The relay is closed . The same goes for closing the relay . It will be “ Crack ” A voice .

————————————————————————————————

So next , We will use MFC To complete such an operation .

Workflow ：1、 Find the serial port --------->2、 Open the serial port ----------->3、 send out “ open ”（ Here are “ Crack ”）----------->4、 send out “ Turn off ”（ It's also here “ Crack ”）-------->5、 Turn off the serial port

First , We create a MFC,

Put this in the dialog 5 Button .

They correspond to each other 5 A function .

The header function is added ：

#include "Dbt.h"
#include "setupapi.h"

————————— Look for the relay ———————————

Then first, look for the relay , Generally, there are two automatic methods ,1、 Traverse USB equipment    2、 Traverse the registry

You can refer to here ：https://blog.csdn.net/wangningyu/article/details/78696221

Traverse the registry , There are also two kinds of ,

One is in   \HKEY_LOCAL_MACHINE\HARDWARE\DEVICEMAP\SERIALCOMM  Look under this path , Only those with device access can be found COM mouth , Can't see who is connected

The other way , Is in   \HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Enum\USB , Use the corresponding PID VID look for （ There is a small problem with this method , That's me USB After the device is plugged into different ports on the computer , Will be registered leaving traces , When I use the program to find it, I can only find the top one , That is, the one who was registered for the first time ）

Everyone wants to know their USB Where is the relay inserted , It's also very simple. , Right click manually “ This computer ” open “ management ”, Click on the left “ Device manager ”, Last point “ port ”

You can see that this relay is COM5.

Specifically, how do you want to find your device , You can choose according to the situation .

I used ：（ If you find something wrong , You can interrupt to have a look ）

/************************************************************************/
//  According to... In the registry PID、VID Information reading 
/************************************************************************/
int COpen_COMDlg::SearchRelayCOM(CString strVidPid)
{
	DWORD	dwIndex = 0;
	HKEY	hKey;
	TCHAR	CommName[_MAX_FNAME] = { 0x00 };
	DWORD	lcbName = _MAX_FNAME;
	DWORD	lValue = MAX_PATH;
	TCHAR	szValue[MAX_PATH];
	LONG	lRtn = 0;
	CString	strTemp, strName, strKey;
	int		nPort = -1;
	int		nStart = -1;
	int		nEnd = -1;

	//  Read PID Corresponding port 
	strTemp.Format(_T("SYSTEM\\CurrentControlSet\\Enum\\USB\\%s"), strVidPid);
	if (RegOpenKeyEx(HKEY_LOCAL_MACHINE, strTemp, NULL, KEY_READ, &hKey) == ERROR_SUCCESS)
	{
		dwIndex = 0;
		while (RegEnumKey(hKey, dwIndex++, CommName, lcbName) == ERROR_SUCCESS)
		{
			//  Read PID Corresponding port 
			strKey.Format(_T("SYSTEM\\CurrentControlSet\\Enum\\USB\\%s\\%s\\Device Parameters"), strVidPid, CommName);
			RegCloseKey(hKey);
			if (RegOpenKeyEx(HKEY_LOCAL_MACHINE, strKey, NULL, KEY_READ, &hKey) == ERROR_SUCCESS)
			{
				lRtn = RegQueryValueEx(hKey, _T("PortName"), NULL, &lValue, (LPBYTE)szValue, &lValue);
				if (lRtn == ERROR_SUCCESS)
				{
					//  Looking for serial port information 
					strName.Format(_T("%s"), szValue);
					
					// Can we find COM（ Theoretically, it can ）
					nStart = strName.Find(_T("COM"), 0);

					//nEnd = strName.Find(_T(")"), 0);
					
					//if (nStart == -1 || nEnd == -1)
					if (nStart == -1)
					{
						RegCloseKey(hKey);
						return -1;
					}

					//strTemp = strName.Mid(nStart + 3, nEnd - nStart);
					strTemp = strName.Mid(nStart+3, 1);
					nPort = _tstoi(LPCTSTR(strTemp));

					RegCloseKey(hKey);
					return nPort;
				}
			}

			lValue = MAX_PATH;
			lcbName = MAX_PATH;
		}

		RegCloseKey(hKey);
	}

	return nPort;
}

———————— Turn on the relay ————————

The previous step , We assume that we already know where the relay is COM The number of the mouth

So here , We can use this code to open a port , Mainly used   CreateFile This function . By the way, I also allocated the buffer size in this function , A timeout structure is also set 、 In the end, I set up DCB.（ You can refer to 《 Computer advanced interface technology 》 This book ）

void COpen_COMDlg::OnBnClickedOpen()
{

	DWORD dwError;
	DCB dcb;
	COMMTIMEOUTS Timeouts;

	CString str;
	str.Format(_T("\\\\.\\COM%d"), RelayPort);
	//str.Format(_T("\\\\.\\COM6"));

	hCom = CreateFile(  str,						//str.GetBuffer(50),
									GENERIC_READ | GENERIC_WRITE,
									0,
									NULL,
									OPEN_EXISTING,
									0, // FILE_ATTRIBUTE_NORMAL | FILE_FLAG_OVERLAPPED,
									NULL);

	if(hCom != INVALID_HANDLE_VALUE)
	{
		GetDlgItem(IDC_OPEN)->EnableWindow(FALSE);
		GetDlgItem(IDC_START)->EnableWindow(TRUE);
		GetDlgItem(IDC_CLOSE)->EnableWindow(TRUE);

		AfxMessageBox(_T(" Serial port opened successfully !"));
	}
	else
	{
		dwError = GetLastError();
		AfxMessageBox(_T(" Failed to open serial port !"));
		return;
	} 

	SetupComm(hCom, 1024, 1024);        // Allocate buffer 


    // Set the timeout structure 
	Timeouts.ReadIntervalTimeout = 1000;
	Timeouts.ReadTotalTimeoutMultiplier = 500;
	Timeouts.ReadTotalTimeoutConstant = 500;
	Timeouts.WriteTotalTimeoutConstant = 500;
	Timeouts.WriteTotalTimeoutMultiplier = 500;
	SetCommTimeouts(hCom, &Timeouts);

    // Configure serial interface （ That is, change the device control block DCB Member variable value of ）
	GetCommState(hCom, &dcb);
	dcb.BaudRate = 9600;
	dcb.ByteSize = 8;
	dcb.Parity = NOPARITY;
	dcb.StopBits = ONE5STOPBITS;
	SetCommState(hCom, &dcb);

}

————————— send out “ open ”——————————

The serial port has been opened by us , Then we'll send it here “ open ”

Use this function ：（ I shared this function from a VR Look at the source code of the device , His code is quite complete , Unfortunately, the web link cannot be found , I'm sorry ）

BOOL COpen_COMDlg::ComSendPacket(unsigned char *sendbuffer, int length)
{
	DWORD dwBytesWrite = length;
	DWORD dwErrorFlags;
	BOOL bWriteStat;

	if (!sendbuffer)
		return FALSE;
	
	ResetEvent(ComWriteOverlapped.hEvent);
	// Clear the output buffer of the serial port 
	PurgeComm(hCom, PURGE_TXABORT | PURGE_TXCLEAR); // Immediately interrupt all writes and return immediately , Even if the write operation has not been completed  |  Clear output buffer 
	ClearCommError(hCom, &dwErrorFlags, &ComWriteStat);

	bWriteStat = WriteFile(hCom, sendbuffer, dwBytesWrite, &dwBytesWrite, &ComWriteOverlapped);
	if (!bWriteStat)
	{
		if (GetLastError() == ERROR_IO_PENDING)
		{
			WaitForSingleObject(ComWriteOverlapped.hEvent, 2000);
		}
		else
		{
			ClearCommError(hCom, &dwErrorFlags, &ComWriteStat);
			// Clear the output buffer of the serial port 
			PurgeComm(hCom, PURGE_TXABORT | PURGE_TXCLEAR); // Immediately interrupt all writes and return immediately , Even if the write operation has not been completed  |  Clear output buffer 
			ResetEvent(ComWriteOverlapped.hEvent);
			AfxMessageBox(_T(" Serial port failed to send data !"));
			return FALSE;
		}
	}

	ClearCommError(hCom, &dwErrorFlags, &ComWriteStat);
	// Clear the output buffer of the serial port 
	PurgeComm(hCom, PURGE_TXABORT | PURGE_TXCLEAR); // Immediately interrupt all writes and return immediately , Even if the write operation has not been completed  |  Clear output buffer 
	ResetEvent(ComWriteOverlapped.hEvent);

	return TRUE;
}

And then we give “ Send on ” Button to add an event ：

void COpen_COMDlg::OnBnClickedStart()
{
	unsigned char OpenRelay[] = { 0xA0, 0x01, 0x01, 0xA2 };
	while (!ComSendPacket(OpenRelay, 4))
	{
		AfxMessageBox(_T(" Resending !"));
	}
	AfxMessageBox(_T(" Serial port sends data successfully !"));
	
}

So this is actually where , You generate a project , use 3 Buttons can be heard “ Crack ” The sound of . At this time, the relay operation indicator will also light up .

——————————— send out “ Turn off ”————————

Basically the same as the previous step , Change to ：

unsigned char CloseRelay[] = { 0xA0, 0x01, 0x00, 0xA1 };
	while (!ComSendPacket(CloseRelay, 4))

that will do .

—————————— Turn off the serial port ——————————

Now suppose we don't want to play this serial port , Then we should get together and break up with him .

void COpen_COMDlg::OnBnClickedClose()
{
	// Disable all events on the serial port  
	SetCommMask(hCom, 0);
	// Clear the data terminal ready signal 
	EscapeCommFunction(hCom, CLRDTR);
	// Discard the output or input buffer characters of the communication resource and terminate the pending read on the communication resource 、 Write operation 
	PurgeComm(hCom, PURGE_TXABORT | PURGE_RXABORT | PURGE_TXCLEAR | PURGE_RXCLEAR);
	CloseHandle(hCom);
	hCom = NULL;
	AfxMessageBox(_T(" The serial port is closed successfully !"));
	return;
}

That's it .

——————————.h In file ————————————

We add ：

private:
	int SearchRelayCOM(CString strVidPid);
	BOOL ComSendPacket(unsigned char *sendbuffer, int length);

	int RelayPort;
	HANDLE hCom;

	OVERLAPPED ComWriteOverlapped;
	COMSTAT ComWriteStat;

public:
	afx_msg void OnBnClickedFind();
	afx_msg void OnBnClickedOpen();
	afx_msg void OnBnClickedClose();
	afx_msg void OnBnClickedStart();
	afx_msg void OnBnClickedOver();

that will do . Let's try it , Listen to the relay crazily “ Crack ”/“ Crack ”/“ Crack ”………

Don't say the , Just finished double 11, Ah …………T T