Real Time Commands; Preferred Implementation - NCR 7158 Owner's Manual

7-100 Chapter 7: Programming Guide

Real Time Commands

These commands provide an application interface to the printer even
when the printer is not handling other commands (RS-232C
communication interface only):
1. Real Time Status Transmission (GS Sequence and DLE Sequence)
2. Real Time Request to Printer (GS Sequence and DLE Sequence)
3. 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 are 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, slip paper jam, thermal printhead overheat, etc.
In addition, there is no way to restart the printer after a paper jam, or to
cancel a slip waiting condition when using the Wait for Slip command.
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.

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 7156 application that already uses the Clear Printer command
or for a new application being developed.