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

EN Programming Tips for Using PJL 11-25
When the printer discards responses, the printer inserts the PJL
unsolicited “printer to host data buffer overflow” message:
CE
CODE=10010
DISPLAY="00 READY"
Note Refer to the “HP LaserJet 4 and 5 Family Comments” section in
Appendix A under “Printer Status Readback” for the exact “printer to
host buffer overflow” message sent by HP LaserJet 4 and 5 printer
families.
The PJL unsolicited “printer to host data buffer overflow” message is
always inserted when the printer discards one or more responses,
even if unsolicited status is turned off.
I/O-switching printers set aside memory for each I/O interface. A
response data buffer overflow on one I/O interface does not mean
another I/O interface will also experience the overflow condition. To
keep the printer's response data buffer from overflowing, applications
should not send more than five queries without accepting the printer's
response to those queries.
The application should always send a PJL ECHO command to
resynchronize with the printer status readback responses (i.e., get rid
of any old responses). However, if the printer's response data buffer is
full and the printer is discarding all future responses, then the host will
receive a PJL unsolicited “printer to host data buffer overflow”
message, but not the PJL ECHO response. Applications must be
designed to handle situations where the printer's response data buffer
overflows and the printer does not provide the expected response, but
instead provides a PJL unsolicited “printer to host data buffer
overflow” message. The application should resend all unanswered
queries whenever the application receives a PJL unsolicited “printer
to host data buffer overflow” message.
Handling Unexpected Printer Responses
Printer sharing devices, like the external printer sharing box or the
MIO card inserted into the printer as shown in Figure 11-1, do not
have sufficient information to allow the printer sharing device to
properly route printer status readback responses to the host
computer (the one running the application that queried the printer). In
particular, unsolicited PJL status is difficult for the printer sharing