Code:
uint8_t   highbyte, lowbyte;
int16_t   intval;

// bytes zu int:
intval = lowbyte + (highbyte << 8);

//int zu bytes:
lowbyte  = intval & 0x00ff;
highbyte = (intval >> 8) & 0x00ff;
hoffe, das stimmt...! 8-)