unsigned short
crc2(unsigned short crc, unsigned char data)
{
   unsigned char i, x16, carry;
 
   for (i = 0; i < 8; i++)
     {
       x16 = (data ^ crc) & 1;
       data >>= 1;
 
       if (x16 == 1)
         {
           crc ^= 0x4002;
           carry = 1;
         }
       else
         carry = 0;
 
       crc >>= 1;
 
       if (carry)
         crc |= 0x8000;
       else
         crc &= 0x7fff;
     }
 
   return crc;
}