Epson A794-D100 - Manual (Page 106)

Chapter 6: Programming Information A794 Owner’s Guide
March 1999 100
Real Time Commands
The Real Time commands provide an application interface to the printer even when the
printer is not handling other commands (RS-232C communication interface only):
♦
Real Time Status Transmission: GS (Hex 1D) Sequence and DLE (Hex 10) Sequence
♦
Real Time Request to Printer: GS (Hex 1D) Sequence and DLE (Hex 10) Sequence
♦
Real Time Printer Status Transmission
The original Printer Status commands, Transmit Printer Status (Hex 1B 76, ASCII ESC
v) and Transmit Cash Drawer Status (Hex 1B 75 0, ASCII ESC u 0) are placed in the
printer’s data buffer as they are received and handled by the firmware in the order in
which they were received. If the paper exhausts while printing data that was in the
buffer ahead of the status command, the printer goes busy at the RS-232C interface and
suspends processing the data in the buffer until paper is reloaded. This is true for all
error conditions: knife home error, thermal printhead overheat, etc. In addition, there is
no way to restart the printer after a paper jam or other error.
The Real Time commands are implemented in two ways to correct these problems. Both
implementations offer the same functionality; which one you choose depends on the
current usage of your application.
Rules for Using Real Time Commands
Three situations must be understood when using real time commands.
First, the printer executes the Real Time command upon receiving it and will transmit
status regardless of the condition of the DSR signal.
Second, the printer transmits status whenever it recognizes a Real Time Status
Transmission command sequence, even if that sequence happens to occur naturally
within the data of another command, such as graphics data.
In this case the sequence will also be handled correctly as the graphics data it is
intended to be when the graphics command is executed from the buffer.
Third, care must be taken not to insert a Real Time command into the data sequence of
another command that consists of two or more bytes.
In this case the printer will use the real time command sequence bytes instead of the
other command’s parameter bytes when finally executing that other command from the
buffer; the other command will NOT be executed correctly.
These three situations generally preclude use of standard DOS drivers for the serial
communication ports when using real time commands.