HP PCL/PJL reference - Printer Job Language Technical Reference Manual

EN Product-Specific Feature Support A-53
Although the printer can accurately select printer languages this way,
we recommend that every job containing printable data include an
ENTER LANGUAGE command to explicitly switch to the correct
printer language. This method improves performance and eliminates
errors in printer language switching. It also guarantees that the
correct language is always selected.
Note The value of the PARALLEL feature as shipped from the factory is
FAST. When a front panel reset is performed, the value is defaulted to
SLOW.
Printer Environment
Unlike most PJL variables, the following environment variable defaults
are not stored in the printer's NVRAM. The primary use is to set
job-specific parameters like those available through the DeskJet
1200C family front panel. This means that they will be reset to the
factory default values after a power cycle.
Printers that support printer environment variables:
HP DeskJet 1600C, 1600M