accessing my com port, writing and reading data

This is a discussion on accessing my com port, writing and reading data within the C Programming forums, part of the General Programming Boards category; im writing a little bit of data to a device connected to COM2 of my computer. then i have to ...

  1. #1
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    accessing my com port, writing and reading data

    im writing a little bit of data to a device connected to COM2 of my computer.

    then i have to wait and collect all the data that comes through it.

    from reading the FAQs and so on, i have gathered that i need to

    A) open the port
    B) handshake and set the correct parameter
    C) send my message through the port
    D) read all messages that come through.

    i wanted to know if i have all the steps down correctly or did i miss any out?

    Code:
    #include <windows.h>
    #include <stdio.h>
    
    int main(int argc, char *argv[])
    
    {
       DCB dcb;
       HANDLE hCom;
       BOOL fSuccess;
       char *pcCommPort = "COM2";  //Set at com 2 for moment
    
       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());
           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());
          return (2);
       }
    
       // Fill in DCB: 9,600 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());
          return (3);
       }
    
       printf ("Serial port %s successfully reconfigured.\n", pcCommPort);
       return (0);
    }
    so far i have only this code to show for it and would like to know if the problem i have is complex and if im doing it right?

    thanks

  2. #2
    and the hat of int overfl Salem's Avatar
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    Seems OK so far....
    If you dance barefoot on the broken glass of undefined behaviour, you've got to expect the occasional cut.
    If at first you don't succeed, try writing your phone number on the exam paper.
    I support http://www.ukip.org/ as the first necessary step to a free Europe.

  3. #3
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    My application freezes b/c I forget to connect a device to the port. Is there way i can check if the com port is open or connected to a device?
    Last edited by NewGuy100; 09-16-2005 at 09:27 AM.

  4. #4
    and the hat of int overfl Salem's Avatar
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    The error status return might say something to that effect.
    Try RTFM
    If you dance barefoot on the broken glass of undefined behaviour, you've got to expect the occasional cut.
    If at first you don't succeed, try writing your phone number on the exam paper.
    I support http://www.ukip.org/ as the first necessary step to a free Europe.

  5. #5
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    Can you elaborate more on that? Whats RTFM?

  6. #6
    and the hat of int overfl Salem's Avatar
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    Read The Fantastic Manual

    http://msdn.microsoft.com/library/de...createfile.asp
    Just in case....
    If you dance barefoot on the broken glass of undefined behaviour, you've got to expect the occasional cut.
    If at first you don't succeed, try writing your phone number on the exam paper.
    I support http://www.ukip.org/ as the first necessary step to a free Europe.

  7. #7
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    Can you give me an example?

  8. #8
    Frequently Quite Prolix dwks's Avatar
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    Of reading?

    Oh, you mean
    The error status return might say something to that effect.
    Well, like this:

    Code:
    int result;
    
    result = thefunction();
    
    if(result == ERRORCODE) report_error();
    You know. Like fgetc() (or getc()).
    dwk

    Seek and ye shall find. quaere et invenies.

    "Simplicity does not precede complexity, but follows it." -- Alan Perlis
    "Testing can only prove the presence of bugs, not their absence." -- Edsger Dijkstra
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