Enabling the Automatic Switch for the Insertion Unit
You can set whether to enable the automatic switch for the insertion unit when the Document Insertion Unit-N is attached. (See "Document Insertion Unit-N.")
1.
Press 
(Settings/Registration).
(Settings/Registration).2.
Press [Function Settings] → [Common] → [Paper Feed Settings].
3.
Press [Auto Switch Inserter Paper Source].
4.
Select [On].
Select [Off] if you do not want to enable the automatic switch.