Echo Response - HP PCL 5 Reference Manual

If the application sends the Echo command and Free Space
command, the printer returns the response to the first Echo command
and Free Space command, along with the response to the second
request. The application will assume that the response received is the
response to its last request. If the application uses random numbers
in the Echo command, this type of mix-up will not occur.

Echo Response

The Echo command returns the following response:
where "
was selected (within the range –32767 to 32767).
For example, if the Echo command,
response would be:
16-26 Status Readback
PCL
ECHO ValueField
" is the Echo command value field value that
ValueField
PCL
ECHO –999
E
*s–999X was sent the status
C
EN