Questions about RS232 communication

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I am writing a C++ program which is used to get the data from a device. The device sends Hex data to the PC. I have written C++ program to get the data and convert it from HEX to ascii. However, i only get some strange characters.

main.cpp
-----------------------------------------------------------------------

C++

#include "windows.h"
#include<iostream>;
#include "fyph.h"
using namespace::std;

int main() 
{
	

    char	*dest;
    int		*destElem;
    int destIndex;
    dest = NULL;
    destIndex = 300;
    destElem = &destIndex;
	

    int n3 = 300;
    HANDLE hSerial;
    hSerial = CreateFile("COM1",
        GENERIC_READ | GENERIC_WRITE,
        0,
        0,
        OPEN_EXISTING,
        FILE_ATTRIBUTE_NORMAL,
        0);
    if(hSerial==INVALID_HANDLE_VALUE){
        if(GetLastError()==ERROR_FILE_NOT_FOUND){
            cout<<"serial port does not exist. Inform user."<<endl;
        }
        cout<<"some other error occurred. Inform user."<<endl;
    }

    DCB dcbSerial2;
    FillMemory(&dcbSerial2,sizeof(dcbSerial2),0);
    dcbSerial2.DCBlength = sizeof(dcbSerial2);
    DCB dcbSerialParams2 = {0};
    dcbSerial2.DCBlength=sizeof(dcbSerialParams2);
    if (!GetCommState(hSerial, &dcbSerialParams2)) {

    }
    dcbSerialParams2.BaudRate=CBR_57600;
    dcbSerialParams2.ByteSize=8;
    dcbSerialParams2.StopBits=ONESTOPBIT;
    dcbSerialParams2.Parity=NOPARITY;

    COMMTIMEOUTS cmt; //create the object
    cmt.ReadIntervalTimeout = 1000;
    cmt.ReadTotalTimeoutMultiplier = 1000;
    cmt.ReadTotalTimeoutConstant = 1000;


    char szBuff3[300]="";
    char szBuff[300]="";
    DWORD dwBytesRead2 = 0while(1)
    {
        if(ReadFile(hSerial, szBuff3, n3, &dwBytesRead2, NULL)==true)
    {

  
	szBuff3[dwBytesRead2]=0;
	dest = hexToAscii(szBuff3,destElem,destIndex);

        dest[dwBytesRead2-1]=0;
	cout<<"dest: "<<dest<<endl;


  
  
        if(!ReadFile(hSerial, szBuff3, n3, &dwBytesRead2, NULL)){
        cout<<"error66"<<endl;
    }
    startval =0;
    finalval =0;
    tt = 0;
    CloseHandle(hSerial);
}

--------------------------------------------------------------------

C++

#include"stdio.h";
#include "malloc.h";
#include<iostream>;
#include <fyph.h>;
using namespace std;





char *hexToAscii (char *srcHex, int *destElements, int srcElements)
{
    int                index, destIndex;
    char    valUpper, valLower, *ascArray;
    int                lowerFlag;
    
    lowerFlag = 0;
    ascArray = NULL;
    *destElements = srcElements/2;
    ascArray = (char *)malloc (*destElements);
    if (ascArray == NULL) {
        return NULL;
    }
    for (destIndex = 0; destIndex < *destElements; destIndex++) {
        for (index = 0; index < 2; index++) {
            if (lowerFlag == 0) {
                if (srcHex[(destIndex * 2) + index] >= '0' && 
                    srcHex[(destIndex * 2) + index] <= '9') {
                    valUpper = srcHex[(destIndex * 2) + index] - '0';
                } else if (tolower (srcHex[(destIndex * 2) + index]) >= 'a' || 
                            tolower (srcHex[(destIndex * 2) + index]) <= 'f'){
                    valUpper = tolower(srcHex[(destIndex * 2) + index]) - 'a' + 10;
                }
                valUpper <<=4;
                lowerFlag = 1;
            } else {
                if (srcHex[(destIndex * 2) + index] >='0' && 
                    srcHex[(destIndex * 2) + index] <= '9') {
                    valLower = srcHex[(destIndex * 2) + index] - '0';
                } else if (tolower (srcHex[(destIndex * 2) + index]) >='a' || 
                            tolower (srcHex[(destIndex * 2) + index]) <= 'f'){
                    valLower = tolower (srcHex[(destIndex * 2) + index]) - 'a' + 10;
                }  
                lowerFlag = 0;
            }
        }
        ascArray[destIndex] = valUpper | valLower;
    }
    return ascArray;
}

Posted 18-Feb-10 0:24am

Kalelaw

Updated 18-Feb-10 7:10am

Richard MacCutchan

v5

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Richard MacCutchan · Answer 1 · 2010-02-18T06:54:00

I have corrected your code formatting above. Also you did not point out where your code is going wrong but I suspect the following two lines are not correct:

C++

} else if (tolower (srcHex[(destIndex * 2) + index]) >= 'a' ||
tolower (srcHex[(destIndex * 2) + index]) <= 'f')
{

the logical operator between the two expressions should be && as both conditions need to be true.

Richard MacCutchan · Answer 2 · 2010-02-18T00:36:00

Your code is largely unreadable as you forgot to put it between <pre></pre> tags; use the 'code block' button. Try and post just the portion that is going wrong, with comments around the actual lines in error. Note please do not post this into a new answer but edit your original question; and use the 'Quick Preview' tab to verify it before posting.

CPallini · Answer 3 · 2010-02-18T08:41:00

Solution 3

In addition to Richard's answer, are you sure the device sends hexadecimal characters? Doesn't it send binary data?
:)

Posted 18-Feb-10 8:41am

CPallini

v2

Richard MacCutchan · Answer 4 · 2010-02-18T10:11:00

I would suggest you replace your read loop with the following

DWORD dwBytesRead2 = 0;
while(1)
{
    if(ReadFile(hSerial, szBuff3, 300, &dwBytesRead2, NULL)==true)	// fixed size 300
    {
        szBuff3[dwBytesRead2]=0;
        dest = hexToAscii(szBuff3,destElem,dwBytesRead2);	// use actual input count
// remove			dest[dwBytesRead2-1]=0;
		
        cout<<"dest: "<<dest<<endl;
			
        if(!ReadFile(hSerial, szBuff3, 300, &dwBytesRead2, NULL))	// fixed size 300
        {
            cout<<"error66"<<endl;
        }
    }
}

And add the following changes to the hexToAscii() function, to allow space for, and add the null terminator

// allocate space plus 1 for null
ascArray = (char *)malloc (*destElements + 1);

ascArray[destIndex] = '\0';    // add this before return

Questions about RS232 communication

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