Numerical controlling method and system

Disclosed are a numerical controlling method and system for controlling a machine such as a machine tool, robot or the like, through an exchange of data between the machine and a numerical controlling apparatus. The system includes conversion circuits incorporated in both of the numerical control apparatus and the machine, the conversion circuits being adapted to convert serial data into parallel data and vice versa; a cable connected between the conversion circuits; an address signal generating circuit adapted to generate an address signal; and a decoder circuit incorporated in the machine and adapted to decode the address signal. The parallel data is converted into serial data so that the exchange of the data is made between the machine and the numerical control apparatus in a bit-serial manner through the cable, so that the machine elements corresponding to the address signals are activated in accordance with the data transmitted bit-serially from the numerical control apparatus or, alternatively, the states of the machine elements corresponding to the address signals are read in a parallel manner and transmitted bit-serially to the numerical control apparatus.