Sorry for my ignorance... but what is "Yang"?
Anyway, it sounds like you have an issue but I am not sure I understand you post. Can you clarify where exactly you measure 40us pulses and how? Also, how is it connected? Can you make a drawing? The motor is supposed to take a step for each pulse signal on PUL, so that seems normal. What "output levels" are you talking about? The only outputs the DQ542MA has is the motor outputs, and that is AC, not DC, and it is NOT measured with reference to the GND.
As I said, I don't understand your post.