HP Color LaserJet 5500 Technical Reference Manual page 202

communication cable is between the printer and those
components).
In summary, an application running on host computer #1
can receive printer responses if the operating system on the
host computer supports bi-directional communication over
the serial I/O interface. The application may have to wait for
the printer's response if the printer is processing a job from
either the Bi-Tronics I/O interface or the MIO interface.
An application running on host computer #2 or #3 may
receive printer responses if the printer sharing box
supports bi-directional printer communication. However,
since the printer sharing box does not have enough
information to route the response to the correct host
computer, the printer sharing box can forward all printer
responses to all attached host computers and let the
application on the host computer ignore any unneeded
printer responses.
Applications on network clients #6 and #7 cannot receive
any printer responses due to the underlying network
operating system. However, the printer sharing box, the I/O
card installed in the printer, and spoolers running on
network servers #4 and #5 can all query the printer and
expect a printer response (although the response will not be
immediate if the printer is processing a print job from a
different I/O interface).
Printer Status
Applications use printer status readback for two primary
purposes (although there are other uses): printer driver
Readback Usage
configuration and monitoring device status. Since printer
configuration does not change often (i.e. the amount of
installed printer memory does not change frequently) using
printer status readback to assist in initial configuration (or
when the printer's configuration changes) is
straightforward. If the application determines printer
status readback is unavailable (discussed in the
"Determining If Printer Status Readback is Available"
section), the application can ask the user for the
information instead of querying the printer.
10-22 Programming Tips