Simple RS232 Question

This is a discussion on Simple RS232 Question within the C++ Programming forums, part of the General Programming Boards category; Hi, could someone please supply me with code for Visual C++ to read from an RS232 connection on Com port ...

  1. #1
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    Question Simple RS232 Question

    Hi, could someone please supply me with code for Visual C++ to read from an RS232 connection on Com port 1 with 9600 baud, even parity, 1 stop bit and 7 data bits. I don't care about writing information I just want to read the data.

    I have a powder metering system controlled via my PC and want to stop it when the reading from the RS232 connected balance hits the level I require.

    many many thanks

    Rich

  2. #2
    and the hat of wrongness Salem's Avatar
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    Win32 treats the serial port as a kind of file
    Start by reading all about createfile
    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.
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  3. #3
    30 Helens Agree neandrake's Avatar
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    So would you use "COM1" as the file to open? I'm just guessing; I remember doing something like that back in days of QBasic
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  4. #4
    Registered User Codeplug's Avatar
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    Here is some code for doing com port I/O.

    gg
    Attached Files Attached Files

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    When I try to compile that I get

    Compiling...
    SFile.cpp
    Linking...
    LIBCD.lib(crt0.obj) : error LNK2019: unresolved external symbol _main referenced in function _mainCRTStartup
    Debug/rs232.exe : fatal error LNK1120: 1 unresolved externals

    If someone could supply me with code which would read from Com port 1, 9600 baud, even parity, 7 data bits and 1 stop bit I promise to thank them forever (and possibly financially if this project works!). Please help!

  6. #6
    Registered User Codeplug's Avatar
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    If you want to use 7 data bits and even parity then you need to make some changes in SFile.cpp:
    Code:
    // Change this line
    static TCHAR MODESETTINGS[]= _T("baud=%d parity=N data=8 stop=1  ");
    // to
    static TCHAR MODESETTINGS[]= _T("baud=%d parity=E data=7 stop=1  ");
    Here is some simple code that demonstrates how to use SFile.
    Code:
    #include <windows.h>
    #include "SFile.h"
    #include <iostream>
    using namespace std;
    
    int main()
    {
        SFile sf;
    
        // open COM1 at 9600, 7E1
        if (!sf.Open(1, 9600))
        {
            cerr << "Failed to open COM1, ec = " << GetLastError() << endl;
            return 1;
        }//if
    
        // read a byte at a time and display it
        // (this should loop forever)
        BYTE b;
        while (sf.ReadByte(b))
        {
            cout << (int)b << endl;
        }//while
    
        return 0;
    }//main
    gg

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    Thanks so much!! Am now able to get the reading from the balance! However, I need to get the reading every 5 seconds or so, which requires sending the command 'S(carriage return)', could you explain simply how the writebyte command works since I cannot get it to work correctly.

    Thanks again, you are a star!

  8. #8
    Registered User Codeplug's Avatar
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    ...since I cannot get it to work correctly.
    Show what you have tried.

    Here is how to use SFile::Write()
    Code:
        char cmd[] = "S\r";
        DWORD written;
        ....
        sf.Write(cmd, 2, written);
    You can use Sleep(5000) to sleep for 5 seconds.

    gg

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    I'm trying to send the command using writebyte since write did not seem to work. I just don't know the exact syntax to use :s

  10. #10
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    I've worked it out!

    Thanks again for your help, if you are ever in Oxford then I owe you at least one pint!

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    Hello Codeplug

    I am using this library thank you very much for providing it. I have tried the example above and it works perfectly. So i have serial data in the form of (40 45 FE 12 34) coming from the serial port and the BYTE b displays them in line (it is pre formatted from my microcontroler) The thing is i would like to store the icoming bytes into a const char* to send it to TCP socket (I allready have that part of code working) Ive tried different manners but it seems i need to convert them to a string or something similar.
    I am sorry i am not very strong in C++ and i have searched a lot i can only ask u now if u can give me a lil clue or an idea of how to perform this im sure this is easy for u
    I thank u very much in advance

  12. #12
    &TH of undefined behavior Fordy's Avatar
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    Please dont open long closed threads, please start a new one.

    CLOSED

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