Samsung SCX-8128NA-XAA - Manual (Page 49)

Media and tray_ 49
1. Press Machine Setup > Tray Settings > Settings > Tray Protection.
2. Choose tray and press the button to activate this function.
Tray priority setting
When you do not select the tray for printing, the tray selected as in the Tray
Priority Setting will be used in order. If the tray does not have the paper on
which you want to print, the machine automatically prints from the trays in
the priority order set.
1. Press Machine Setup > Tray Settings > Settings > Tray Priority
Setting.
2. Press a tray, and give priority in the order for printing job using UP and
Down Arrows.