M-S Cash Drawer A794 - Manual (Page 115)

Chapter 6: Programming Information A794 Owner’s Guide
December 1999 110
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 Batch Mode Printer Status commands 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, when using Batch Mode Status commands.
The Real Time commands are implemented in two ways in order to overcome the
limitations of Batch Mode Status commands. Both implementations offer the same
functionality; which one you choose depends on the current usage of your application.
Preferred Implementation
For a new application the GS (1D) sequences are recommended to avoid possible
misinterpretation of a DLE (0x10) sequence as a Clear Printer (0x10 0, ASCII DLE NUL)
command.
An application using these GS (1D) sequences, does not need to distinguish for the
printer between the new real time commands and the Clear Printer command. This
implementation is ideal for an existing A756 application that already uses the Clear
Printer command or for a new application being developed.
Alternate Implementation
The alternate implementation uses the DLE (0x10) sequences as implemented on other
printers. An application using these DLE (0x10) sequences and the original A756 Clear
Printer command (0x10) must distinguish for the printer between the new real time
commands and the Clear Printer command by adding a NUL (0x00) to the Clear Printer
command.
An application using these DLE (0x10) sequences must also send the second byte of the
sequence within 100 milliseconds of the first, to prevent the first byte being mistaken for
a Clear Printer command.