Single-chip microcomputer and motor driver module of ground, light coupling is doesn't work?

Had better not altogether..
http://www.siliconray.com/stm32-q-sys-summer-board-cc2500-wireless-module.html
Light coupling basically is an electrical isolation effects, but in the common in the circuit to still can rise to another role is light on both sides of the coupling can solve level transformation, such as 5 V system to the 3.3 V system, or vice versa. But the light of coupling use is used for electrical isolation, if use light coupling, and the total land, the light coupling meaningless, level conversion can use other methods.
Motor driver circuit, the start of the motor to the influence of the single chip microcomputer is very serious, the proposal does not altogether, send a single chip microcomputer starts commands in a suspended state after a period of time, or nop instructions, avoid voltage is not stable stage, started to work.