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

11-18 Programming Tips for Using PJL EN
Requesting Printer Status
When querying the printer for status, the response is not immediate.
Wait a fixed amount of time for a response and then time out. If the
printer is still working on a previous print job, it may take a while
before a response is received.
Your application should be able to discard unexpected status, such as
unsolicited status, and discard unrecognizable lines. Lines within the
PJL status response begin with a specific keyword, as described in
the command description in Chapter 7, and end with the <CR><LF>
control codes. Future printers may support new keywords in the PJL
status response. Your application should ignore those lines which it
does not understand.
Using Status Readback in a Multi-User System
The printing system consists of all components involved in the
process of turning an application document into a printed sheet of
paper. Common printing system components include the host
computer, applications on the host computer, the operating system
used by the host computer, the cable connecting the host computer to
the printer, and the printer. Other printing system components can
include printer sharing boxes, network servers, spoolers running on
network servers, and I/O cards installed in the printer. For printer
status readback to be useful, all components must be bi-directional.
Some operating system environments, like Microsoft's Windows,
provide the components that interact with the printer so Windows
applications generally do not need to support printer status readback.
The components that may generate printer queries include the host
application, the printer sharing box, the network spooler, and the I/O
card installed in the printer. Printer status readback can allow many
printing system components to function more effectively, not just the
host application. For example, a network I/O card may inject a PJL
JOB command at the beginning of each job and a PJL EOJ command
at the end of each job. Using unsolicited PJL job status, the I/O card
could sent a network packet to an application on the client that
supplied the job, notifying the user the job had been printed. Printer
status readback allows many printer system components to solve
user's needs.