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

EN Introduction to PJL 1-5
PCL Jobs
When non-PJL printers receive PCL jobs, any PJL commands that
precede the initial PCL printer reset command (<ESC>E) print as
ASCII text. When the initial printer reset command is received, it
causes a page eject and the PCL job begins on a new page. The end
result is a page or more of PJL commands followed by the PCL job,
and possibly followed by more PJL commands. The PCL job should
print as it would without any PJL commands, as long as the PCL
portion of the job begins and ends with a PCL printer reset command.
However, a page of PJL commands printed before and probably after
the PCL job can be expected.
For those PCL applications that do not begin with a PCL printer reset
command (or another PCL command that forces a page eject when
preceded by printable data), the PJL commands are printed as ASCII
text on the same page as the PCL job. A good portion of the job may
be unusable due to unpredictable page breaks and overprinted text
on the first page.
PostScript Jobs
When non-PJL printers are running in PostScript mode, PJL
commands cause a PostScript error and prevent the job from printing.
Pressing the printer's Continue key removes the error message, but
the error causes the printer to discard the PostScript job.
Other Printer Languages
PJL code is interpreted differently when running different printer
languages on non-PJL printers. To avoid printing problems, do not
use PJL commands when printing to any non-PJL printer, regardless
of which printer language is used.