A（Answers）

This is to prevent distortion of the waveform in the transmission line due to multiple reflection in multi-node connections. Since MECHATROLINK-Ⅱ systems use bus connections, it is ideal to have high impedance for the input impedance of the differential signals of the modules seen from the transmission line side. However, since in reality the input impedance of the differential signals of the modules is several thousands of ohms, the characteristic impedance of the transmission line deteriorates at the module end, and considerable reflection occurs.
If the cable is 0.5 m or longer the reflection disperses and can be ignored, but if it is shorter than this the reflection waves become superimposed and affect the transmission line. For this reason the minimum cable length is stipulated as 0.5 m.