Continious to alternative rotation using only one link rod.

Greetings everyone,
I am having a problem understanding how it is possible to transform continious to an alernative rotation using only 1 linking rod for each part.
The link rod (12) is connected to the eccentric from one side and to the edge of part (8) ,

Part 8 is alternatively rotating (in its center) in a limited angle

As described in the exploded view below.
Please i am unable to proceed unless i fully understand this point.
Thanks in advance.

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