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

EN Status Readback Commands 7-3
Printer Status Requirements
To receive status information from the printer, the application must
have program code that handles the status information sent from the
printer.
Synchronizing Status Readback Responses
Status responses are directed to the printer's I/O port from which the
request is received. When using status readback, applications must
synchronize status messages to ensure that status responses are
indeed the requested status. To clear any possible unread status
responses requested by previous applications, upon starting up, an
application should use the ECHO command as described in the
ECHO command section later in this chapter.
If unsolicited status is enabled, applications should properly handle
receiving unsolicited status responses at any time. In particular, be
aware that applications may receive an unsolicited status response
after requesting printer status information.
The application and printer must be in a printer environment that
supports two-way communication between the application and the
printer. Printer sharing devices, networks, and other printing system
components may not support this bi-directional communication.
(Refer to “Using Status Readback in a Multi-User System” in
Chapter 11.)