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POSerial port: Read data problem with loopback, not reading anything
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copied!<p>This problem has been asked many times, I read all the answers but still not able to figure out the problem.</p> <p>I have set up connection with COM1 port Wrote data to COM1 port using WriteFile Now I am trying to read data from the port using ReadFile but it is not reading anything. I have hard ware loopback the 2nd and 3rd of RS232 so that input can be read as output</p> <pre><code>#include <windows.h> #include <stdio.h> # include <tchar.h> int main(int argc, char *argv[]) { DCB dcb; HANDLE hCom; BOOL fSuccess; char *pcCommPort = "COM3"; hCom = CreateFile( _T("COM3"), //pcCommPort, GENERIC_READ | GENERIC_WRITE, 0, // must be opened with exclusive-access 0, // no security attributes OPEN_EXISTING, // must use OPEN_EXISTING FILE_ATTRIBUTE_NORMAL, // not overlapped I/O NULL // hTemplate must be NULL for comm devices ); if (hCom == INVALID_HANDLE_VALUE) { // Handle the error. printf ("CreateFile failed with error %d.\n", GetLastError()); } // Build on the current configuration, and skip setting the size // of the input and output buffers with SetupComm. fSuccess = GetCommState(hCom, &dcb); if (!fSuccess) { // Handle the error. printf ("GetCommState failed with error %d.\n", GetLastError()); } dcb.BaudRate = 9600; // set the baud rate dcb.ByteSize = 8; // data size, xmit, and rcv dcb.Parity = NOPARITY; // no parity bit dcb.StopBits = ONESTOPBIT; // one stop bit fSuccess = SetCommState(hCom, &dcb); if (!fSuccess) { // Handle the error. printf ("SetCommState failed with error %d.\n", GetLastError()); } printf ("Serial port %s successfully reconfigured.\n", pcCommPort); char Buff[] = "Hello"; char Buff2[50] = {}; DWORD dwNumBytesWritten; DWORD dwBytesTransferred; printf("\n\n\n\n\n\n Start writting ! \n"); WriteFile (hCom, // Port handle Buff, // Pointer to the data to write sizeof(Buff), // Number of bytes to write &dwNumBytesWritten, // Pointer to the number of bytes written NULL // Must be NULL for Windows Embedded CE ); printf("\n Bytes Written to the terminal "); for( int j=0; j<dwNumBytesWritten; j++) printf("%c",Buff[j]); printf("\n Byte length %d \n", dwNumBytesWritten); printf("\n\n\n\n\n\n Start reading !\n"); ReadFile (hCom, // Port handle Buff2, // Pointer to data to read dwNumBytesWritten, // Number of bytes to read &dwBytesTransferred, // Pointer to number of bytes read NULL // Must be NULL for Windows Embeddded CE ); for( int j=0; j<dwNumBytesWritten; j++) printf("%c",Buff2[j]); printf("\n BytesRead from the terminal:%d \n",dwBytesTransferred); CloseHandle(hCom); int num; scanf("%d", &num); } </code></pre> <p>The program is not returning any error code, but it continously waits to read data from COM1 port and never receives anything. I am stuck as I can't really decifer where the problem is. Any pointers will be helpful.</p> <p>Thanks,</p> <p>Yogesh</p>

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