Samsung PN51E6500EFXZA - Manual (Page 175)

N The USB device must be connected
to your TV before you can select
USB .
N If you select a source other than TV
or USB , you must:
ΠHave a cable or satellite set-top
box attached to that source.
ΠSet the set-top box to the
channel you want to watch when
the TV goes on.
ΠLeave the set-top box turned on.