HP PCL/PJL reference (PCL 5 Printer Language) - Technical Reference Manual Part I

4-10 PCL Job Control Commands EN
Duplex Page Side Selection Command
The Duplex Page Side Selection command causes a Form Feed and
designates which side of the sheet to print.
The ability to skip a page while duplexing may be required at certain
locations in a document. For example, a chapter typically begins on
the front side of a page.
?&a#G
# = 0 - Select next side
1 - Select front side
2 - Select back side
Default = 0
Range = 0-2 (All other values ignored)
If this command is received by a printer which does not have duplex
or if duplexing is not enabled, these commands just eject the current
page (sheet), positioning the cursor at the default position on the next
page.
Example
To print on the front side of a page, regardless of the current side,
send the following:
?&a1G
In this example, if the printer is currently formatting a front side, it will
stop formatting, eject that page (sheet, skipping the back side), and
begin printing on the next front page.