HP 5961-0509 manual Status Readback Programming Hints

Status Readback Programming Hints

The following hints can assist in using the status readback feature.

zPCL status readback is useful during the development of applications. Status readback allows you to determine that fonts, macros, user-defined patterns, and symbol set resources you have downloaded were accepted by the printer.

zIf the printer does not contain sufficient memory to accept a downloaded entity, the printer discards the data. Status readback can be used to determine if the printer accepted a downloaded entity.

zStatus responses are directed to the printer’s I/O port from which the request is received. If the status is not read and the printer switches to another I/O port, the status response is not directed to that port. The status response returns if the printer switches back to the original port (see note on following page).

zYour application should work correctly when an unexpected status response is received. For example, when requesting a PCL status, it is possible that PJL could return an unsolicited status response, if PJL is enabled.

•All PCL status responses begin with the “PCL” header and end with the <FF> control code. When reading PCL status responses, your application should be able to read all the data between the “PCL” header and the <FF> control code. It should ignore any other status response syntax.

•Lines within the PCL status response begin with a specific keyword (those described in this chapter) and end with the <CR> and <LF> control codes. Future printers may support new keywords in the PCL status response. Your application should be designed to ignore those lines which it does not understand.

zThe first PCL status readback command an application should send is the PCL Echo command. A random number should be generated for the value field each time the command is sent. Your application should ignore all printer status readback data until the PCL Echo status readback response is received, echoing the number the application sent.

zTo clear any possible unread status responses from previous applications, an application, upon starting up, may want to read any pending responses until they are cleared from the printer.

EN Status Readback Programming Hints 16-27