xmodem crc

hello,

I want to send a file with xmodem crc.
After the first "C" from the reciever, I prepare the first packet and send it to the reciever. But then I get another "C" instead a "NAK" or an "ACK".

Has anybody an idea, or a working example for windows/dos with the source code.

Thanks a lot.

cu hick.hack

yes, I know already what the xmodem protocol is for use.
But it dosn't work in my code.
Want I want is to send a file is the same way like hyperterminal.

Here is my code for preparing the xmodem block.

Code:

switch (szBuffer[0]) 
{
  case 'C':  // 'C' means the reciever want data in XModem CRC
  packetno = 1;
  filepointer = fopen("start.sre", "rb"); // open the file for binary read

  while (!feof(filepointer)) 
  {
    // xbuff[0] = SOH; bufsz = 128;  // 128 Byte block size
    xbuff[0] = STX; bufsz = 1024;  // 1024 Byte block size
    xbuff[1] = packetno;
    xbuff[2] = ~packetno;
                        
    memset (&xbuff[3], 0, bufsz);
    numread = fread( &xbuff[3], sizeof( char ), bufsz, filepointer);
    if (numread < bufsz) xbuff[3+numread] = CTRLZ;
    
    // calculate the crc checksum                    
    unsigned short ccrc = calcrc((char *) &xbuff[3], bufsz);
    xbuff[bufsz+3] = (ccrc>>8) & 0xFF;
    xbuff[bufsz+4] = ccrc & 0xFF;

    do
    {
      // the serial class is from this homepage
      // http://home.ict.nl/~ramklein/Projects/Serial.html
      serial.Write(&xbuff[0], bufsz + 5);  
      serial.Read(szBuffer, sizeof(szBuffer)-1, &dwBytesRead);
      if (dwBytesRead > 0) 
      {
        switch (szBuffer[0]) 
        {
        case NAK:   printf ("%d NAK recieved \n", szBuffer[0]);
                           break;
        case ACK:   printf ("%d ACK recieved \n", szBuffer[0]);
                           break;
        case CTRLZ: printf ("%d Cancel by remote \n", szBuffer[0]);
                           break;
        default:    printf ("%d Unknown \n", szBuffer[0]);
                         break;
        }
      }
    } while ((szBuffer[0] != ACK));

    // If sending was succesfully
    packetno++;
    if (packetno >= 256) packetno = 0;
 }

  // the whole file was send
 fclose (filepointer);
}

and here is the code for the calccrc function

Code:

int calcrc(char *ptr, int count)
{
    int crc, i;

    crc = 0;

    while (--count >= 0) {
       crc = crc ^ (int)*ptr++ << 8;

       for (i = 0; i < 8; ++i)
           if (crc & 0x8000)
               crc = crc << 1 ^ 0x8408;
           else
               crc = crc << 1;
       }
   return (crc & 0xFFFF);
}

thanks for your help