HP Color LaserJet 5500 Technical Reference Manual page 207

There is also a chance the PJL ECHO response will never
by sent by the printer, due to overflowing of the printer's
response data buffer as discussed in the following section.
Response Data
The printer contains a limited amount of memory. It is
possible for an application to fill all available printer
Buffer Overflow
memory with printer status readback responses that have
not yet been sent to the host computer, simply by sending
many queries and never accepting the responses from the
printer. Also, if an application enables unsolicited status
and never accepts responses, the printer's response data
buffer can overflow. The printer limits the amount of
memory allotted to hold responses, and when that memory
is full (and the host has not recently accepted any
responses), the printer discards all future responses until
the host accepts the currently queued responses in the
printer.
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.
Programming Tips 10-27