Procedure for two-sided combine (classic)
Press [Original Settng].

Press [Original Size].
Specify the original size, and then press [OK].
Press [Original Orientation].
Select original orientation.

Press [OK].
Press [Dup./Combine/Series].

Press [Combine].

Select [1 Sided] or [2 Sided] for [Original:].

Press [Combine 2 Sides].
Press [Orientation].

Select [Top to Top] or [Top to Bottom] for [Original:] if the original is two-sided.
Select [Top to Top] or [Top to Bottom] for [Copy:], and then press [OK].
Select the number of originals to combine.

Press [OK].
Select the paper tray.
Place the originals, and then press [Start].