The reference point is the reference point for the CNC machine. Many functions of the CNC system are based on the reference point. CNC machine tools generally require the power-on first to perform the reference point operation. The SINUMERIK 802S/802S base line is an economical CNC system with stepper drive. The reference point is achieved by installing a proximity switch to detect the zero pulse. In practical applications, there are many problems due to the quality of the proximity switch, installation position, parameter adjustment, etc., which causes the 802S system to fail to return to zero normally. For example, sometimes there is a secondary zero return, a wrong circle or a reference point collapse phenomenon. Affect the normal use of the user's machine tool.