*b = ((int)EEPROM_Read(a) << 8) | (int)EEPROM_Read(a+1);
や
*b = ((long)EEPROM_Read(a) << 24) | ((long)EEPROM_Read(a+1) << 16) | ((long)EEPROM_Read(a+2) << 8) | (long)EEPROM_Read(a+3);
みたいに書かないといけない。