Wincor Nixdorf TH250, Programmer'S Manual

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TH250 Programmer’s Guide
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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 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 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.
Rules for using real time commands
Three situations must be understood when using real time commands.
First, the printer executes the real time command within a few msec of detecting it in the input
buffer 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.
Moving data through the buffer
Applications should not let the buffer fill up with real time commands when the printer is busy at
the RS-232C interface. A busy condition at the RS-232C interface can be determined by bit 3 of the
response to 1D 05, or 1D 04 1, or 10 04 1. The reason for a particular busy condition can be
determined by other responses to 1D 04 n or 10 04 n.
Although the printer responds to real time commands when it is busy, it will place them into the
buffer behind any other data there, and flush them out in the order in which they were received.