After much efort I have been able to read and write binary data (
including NULLs ) in the serial port with BCB5
and the MSComm32 component from VB6.

Here there is an example of reading :

/* This is the function called on Comm event.
 */
void __fastcall Tdiso::CommPortComm(TObject *Sender)
{
    switch ( CommPort->CommEvent )
    {
        /* You may place code to take care of eache event.
         */
             case comBreak
             case comEventCDTO :
             case comEventCTST:.
             case comEventDSRTO:
             case comEventFrame
             case comEventOverrun:
             case comEventRxOver:
             case comEventRxParity:
             case comEventTxFull:
             case comEventDCB:
                       Received->Caption = "Communication error";
            break;

            /* Data received take it ( if you can )
            */
   case comEvReceive:
                {
                        OleVariant Hope;
                        AnsiString One;
                        int ReceivedBytes = CommPort->InBufferCount;
                        int ReadedBytes = 1;
                        CommPort->InputLen = ReadedBytes;
                        unsigned char raw_data[BUFFER_SIZE];
                        /* You must take the data out one by one or you
will lose all the data after first null caracter.
                         */
                        for ( int i = 0;i < ReceivedBytes;i++ )
                        {
                                Hope = CommPort->Input;
                                WideString Needed = Hope;
                                One = Needed;
                                memcpy (  (char *)&raw_data[i], ( char *
)One.c_str(), 1 );
                        }

Although it may seem a bit complicated you must do it in this way or
risk to hung the BCB or even the windows.

Here there is an example of writing :

   SendBuffer[0] = 0x01;
   SendBuffer[0] = 0x03;
   SendBuffer[0] = 0x0a;
   SendBuffer[0] = 0xd1;
   SendBuffer[0] = 0x00;
   SendBuffer[0] = 0x00;
   SendBuffer[0] = 0x02;
            .
            .
            .

 AnsiString OutData = "";;
 SendBuffer[num_bytes] = 0x00;
    /* This is very tricky but you must do it or no caracter will be
send after the first NULL.
     */
   OutData..SetLength ( num_bytes+1 );
   memcpy ( (char * )OutData.c_str (),(char *)&SendBuffer[0],
num_bytes+1 );
   OutData.SetLength ( num_bytes );
   CommPort->Output = OutData;

Although it may seem a bit complicated you must do it in this way or
risk to hung the BCB or even the windows.

I have tested this example and has been working sending and reciving 24
hours without a problem.

To find this solution I researched the borlands newsgroup and taked some
hint here and there,
so I think it fair to post it here may it help someone.

In the future please do not post in HTML.  This goes against the rules of use
for these newsgroups and can result in your post being canceled
(www.borland.com\newsgroups).  Thank you.

--
Jeff Overcash (TeamB)
      (Please do not email me directly unless  asked. Thank You)
A human being should be able to change a diaper, plan an invasion, butcher
a hog, conn a ship, design a building, write a sonnet, balance accounts, build
a wall, set a bone, comfort the dying, take orders, give orders, cooperate, act
alone, solve equations, analyze a new problem, pitch manure, program a computer,
cook a tasty meal, fight efficiently, die gallantly.  Specialization is for
insects.   (RAH)