problem in the serial progrmming code!!!

Question

Hello, I am using Windows 7, the code i have written for serial programming is not receiving the data transmitted :when I connected a null modem to the serial port to read the string i wrote to the serial port but nothing is read on serial port. The program copiles, builds and executes but i get error reading. 
can anybody help me please !!!

The code i wrote is:

#include <windows.h>
#include <stdio.h>

int nread,nwrite;
int main(int argc, char *argv[])
{
   DCB dcb;
   HANDLE hCom;
   BOOL fSuccess;
   char *pcCommPort = "COM2";
   char *words, *buffRead, *buffWrite;
   DWORD dwBytesWritten, dwBytesRead;
 
   hCom = CreateFile( pcCommPort, GENERIC_READ | GENERIC_WRITE, 0,    // must be opened with exclusive-access
                    NULL, // no security attributes
                    OPEN_EXISTING, // must use OPEN_EXISTING
                    0,    // 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());
       getch();
       return (1);
   }
 
   // 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());
      getch();
      return (2);
   }
 
   // Fill in DCB: 57,600 bps, 8 data bits, no parity, and 1 stop bit.
 
   dcb.BaudRate = CBR_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());
      getch();
      return (3);
   }
 
   printf ("Serial port %s successfully reconfigured.\n", pcCommPort);
  
   
//****************Write Operation*********************//
//words = "This is a string to be written to serial port COM1";
words = "Ab";
nwrite = strlen(words);
 
buffWrite = words;
dwBytesWritten = 0;
 
if (!WriteFile(hCom, buffWrite, nwrite, &dwBytesWritten, NULL))
{
printf("error writing to output buffer \n");
}
printf("Data written to write buffer is \n %s \n",buffWrite);
 
 
 
//***************Read Operation******************//
//buffRead = 0;
dwBytesRead = 0;
nread = strlen(words);
printf ( "Nread = %d\n",nread );
 
if (!ReadFile(hCom, buffRead, nread, &dwBytesRead, NULL))
{
printf("error reading from input buffer \n");
}
else
{
printf("Data read from read buffer is \n %s %d\n",buffRead,dwBytesRead);
}
getch();
 
CloseHandle(hCom);  
 
return (0);
 
}

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BAA

Answer 1

You don't have a valid read buffer.  The buffRead variable is an uninitialized pointer containing some garbage value.  Windows expects it to be the address of some memory that you have allocated.  Try this instead:

char buffRead[256];

Answer 2

Ya it worked but if there is no data on RXD pin compiler is not executing readfile function and remaining too. readfile Code is here... PLease help me..

if (!ReadFile(hCom, &buffRead, nread, &dwBytesRead, NULL))

{ printf("error reading from input buffer \n"); getchar();

}

else

{

printf("Data read from read buffer is \n%s %d\n",buffRead,dwBytesRead);

getchar();

}

CloseHandle(hCom);

getchar();

return (0); }

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BAA

Answer 3

Ya it worked but if there is no data on RXD pin compiler is not executing readfile function and remaining too.

Unless you have somehow arranged for your source code to be provided on the serial port, it's not the compiler which is 'not executing readfile function' here, but the running program itself.

I  interpret your  phrase 'not executing readfile function and remaining too' as meaning that the ReadFile is not returning.

This is normal behaviour for a synchronous ReadFile call on such a device.  It won't return until there is some data to read (in this case, on RXD pin).  If you want asynchronous behaviour, you need to use ReadFile's Overlapped mechanism (the final paramater which you have set to NULL), or that of ReadFileEx.

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Answering policy: see profile.

Answer 4

 It won't return until there is some data to read (in this case, on RXD pin).  If you want asynchronous behaviour, you need to use ReadFile's Overlapped mechanism (the final paramater which you have set to NULL), or that of ReadFileEx.

Besides of the Overlapped thing, you can specify read timeout, and any available data (or none) will be returned. See this. 

-- pa

Answer 5

Have you try to disable control in the DCB structure to configure your port:

fRtsControl 

fRtsControl

fParity

and all other parameters ...

http://msdn.microsoft.com/en-us/library/windows/desktop/aa363214(v=vs.85).aspx

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Delphine GARRO

Answer 6

Another error is in the printf of buffRead. The received string is not nul terminated, so printf will attempt to print more than just the number of bytes received.  This will print garbage and it might also cause an access violation. After receiving some bytes you should add

buffRead[dwBytesRead] = 0;

to properly nul terminate the string.

 

Answer 7

Thanks alot for your suggestions Scott...

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BAA

Answer 8

Thank you Pavel... I'll work on it..

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BAA

Answer 9

Thank you for the information David...

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BAA

Answer 10

Have you the solution ?

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Delphine GARRO

Answer 11

Yeah Delphine thank you for the help...

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BAA