Kyocera DU-21 Manuel D'utilisation page 26

Manual feeding
Duplex printing is not available if paper is fed manually from the printer's manual
feed tray or using the optional envelope feeder. If the paper is fed manually while
the duplexer is activated, the printer automatically deactivates the duplex mode
and delivers all output pages to the face-up tray.
Mode selection by command
As an alternative to the control panel selection procedure described on page 9,
you can select duplex printing and the binding mode setup using certain
PRESCRIBE and PCL commands. These commands also provide certain
functions that are not available from the control panel.
The PRESCRIBE duplex control commands and their functions are:
DUPX (select/deselect DUPleX mode)
DXPG (select DupleX PaGe side)
The PCL commands provide the same functions as the PRESCRIBE commands
listed above. However, unlike the PRESCRIBE commands (which can be used in
any printer emulation mode), the PCL commands are only effective while using
the printer in the HP LaserJet emulation (PCL) mode.
The PCL duplex control commands and their functions are as follows.
<Esc>&l#S (select/deselect duplex mode)
<Esc>&a#G (select duplex page side)
PRESCRIBE commands are described in detail below.
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