Optional Lower Cassette - Epson AcuLaser C900 Reference Manual

4. Close the MP tray flap and set the MP tray cover.
5. Make sure the MP Tray Size setting in Printer Setting on the
printer driver's Optional Settings menu matches the media
loaded.
Note:
To print on the back side of previously printed paper, use the MP
tray. The optional Duplex Unit cannot be used for this purpose.
Be sure that you do not add paper while printing.

Optional Lower Cassette

Note:
To use the optional 500-Sheet Paper Cassette Unit, select it in the printer
driver's Optional Settings menu after installing it on the printer.
Follow these steps to load paper into the optional lower cassette.
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Paper Handling