User guide

A795 User Guide: Programming Supplement
Chapter 4: Programming commands
74
Status
Status command introduction
The A795 has three methods of providing status to the application. These methods are through
batch status commands, real time status commands and unsolicited status mode. An application
may use one or more of these methods to understand the current status of the printer. A brief
description of each of these methods follows.
Batch status commands – These commands are sent to
the printer and stored in the printer’s buffer. Once the
printer has processed all the previous commands these
commands are processed and the proper status is returned
to the application. In the event a condition causes the
printer to go BUSY, it stops processing commands from
the printer buffer. If a batch status command remained in
the buffer during this busy condition, it would not be
processed. In fact, no batch commands are processed
while the printer is in this state.
Real-time commands – These commands are sent to the
printer and are NOT stored in the printer’s buffer. Instead,
they are acted on immediately (regardless of the printer’s
BUSY status) and their response (if any) is returned to the
application. This gives the application the ability to query
the printer when it is in a busy state in order to correct
whatever fault has occurred.
Unsolicited status mode – This mechanism allows
the application developer to program the printer to
automatically respond with a four byte status when
certain conditions in the printer change.
Please see the subsequent sections for a more detailed
description of these status commands. At the end of this
status commands section is a page entitled “Recognizing
data from the printer”. This describes how to interpret
what command or setting (in the case of unsolicited status
mode) triggered a response from the printer.
Batch mode
For RS-232C printers, these commands enable the printer
to communicate with the host computer following the
selected handshaking protocol, either DTR/DSR or XON/
XOFF. They are stored in the printer’s data buffer as they
are received, and are handled by the firmware in the order
in which they are received.
When a fault occurs, the printer will go busy at the
RS-232C interface and not respond to any of the batch
mode printer status commands. If the fault causing the
busy condition can be cleared, such as by loading paper,
or letting the thermal printhead cool down, the printer will
resume processing the data in its receive buffer.