Keypad 8400 motec freezes when being attached

Question: 

When attaching the keypad to an 8400 motec, the keypad freezes in the initialisation step. How can this maloperation be avoided and how can it be reset?

 
Answer:
Be careful not to tilt the keypad when attaching it to the 8400 motec.
If the keypad freezes during initialisation, remove it from the 8400 motec, wait for at least 3 seconds and attach it again correctly.

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