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

EN Programming Tips for Using PJL 11-19
Example Printing System
Figure 11-1 contains an example printing system. The print system
contains one I/O-switching LaserJet printer which is connected to
seven computers. Host computer #1 is connected via the serial I/O
interface. Host computers #2 and #3 are connected through an
external printer sharing box that also buffers print job data. The
printer sharing box is connected to the printer through the IEEE-1284-
compatible I/O interface. Network servers #4 and #5 spool print jobs
from network clients #6 and #7.
Although all the network clients and spoolers are connected to the
same network cable as the printer, only the two network servers are
capable of communicating directly with the printer. In this example,
the network clients spool print jobs to a network server; they can not
interact directly with the printer.
Given the printing system as shown in Figure 11-1, not all of the
printing system components can query the printer and expect a
response back.
Printer Status Readback and Printer Sharing
Host computer #1 is directly connected to the printer via the
bi-directional serial I/O link. If the software on the host computer
supports bi-directional printer communication, applications on host
computer #1 can expect the printer to respond to queries. However, at
the time an application on host computer #1 requests information, the
printer may be processing a print job from a different I/O interface, so
the response to host computer #1's query may be delayed, as
described in the “Printer Status Readback and Printer I/O Switching”
section in this chapter.
Host computers #2 and #3 are connected to the printer via an
external printer sharing box that buffers data. If the printer sharing box
was not designed to support bi-directional communication with the
printer, then applications on host computers #2 and #3 will not be
able to receive printer status readback information. However, since
the printer sharing box is connected to the printer via the Bi-Tronics
I/O interface, which does support bi-directional communication, it is
possible for printer sharing boxes to be designed to support printer
status readback. In fact, the printer sharing box itself may be able to
inject a “print job” to query the printer for specific information.
External printer sharing boxes can be designed to support sending
data from the printer to the host computer. However, the printer
sharing box has to determine which host computer should receive the