Lantronix ETS Reference Manual - 2.11 Postscript
PostScript
Concepts
2-18
See Set/Define Server Session Limit on page 12-80 and Set/Define Port Session Limit on page 12-50 for
more information.
2.11 PostScript
Many printers (including all LaserWriters and other AppleTalk compatible laser printers) use a printing
language called PostScript. Unlike other printer protocols, which typically accept ASCII characters and
print them verbatim, PostScript is also a programming language. Shapes and fonts can be defined as
routines and re-used on successive pages, multiple fonts and copies can be printed, and text and diagrams
can be rotated and shifted on pages.
PostScript is also an interactive language, where the printing host can query the printer for its knowledge
about fonts and software versions. If the host expects to receive data from the printer (as is the case for all
AppleTalk printing), the printer must support Bitronics mode and be connected to a bidirectional port such
as one on the ETS. PostScript printing from UNIX, LAT, and NetWare hosts, where bidirectional data flow
is not a requirement, can generally use any parallel port.
PostScript is a verbose language; it is recommended that the printer and ETS use a baud rate of at least 9600
to communicate over serial lines. A baud rate of 38400 or better is strongly recommended for high-output
duty; see the printer’s documentation for information on changing the serial speed. Also, many PostScript
jobs contain 8-bit characters. The ETS is configured for 8-bit characters, but if the printer is not (the default
on many laser printers is 7-bit), some characters will be printed incorrectly. See your printer’s
documentation for details on how to change the character size setting.
Due to the interactive nature of PostScript, it is possible for the printer and host to get out of synch in their
communication. Since the printer “interprets” the entire PostScript job and then prints the pages, it is
possible for the ETS to complete the transfer and accept a new job while the printer is still digesting the last
job. For this reason, an end-of-job character (ASCII 0x4 or Ctrl-D) is used to end all PostScript jobs.
Typically the host will send one at the end of the job and the printer will reply with one when it is done
processing the job. For information on end-of-job characters, see Set/Define Service EOJ command on
page 12-86.
The ETS will force a Ctrl-D character when PostScript is enabled on the appropriate service and wait for
one in return. Therefore, enabling PostScript is strongly recommended for all PostScript printer
applications. It guarantees that the printer is ready to accept new data when the job actually starts. Job loss
and printer hangs are the usual result if PostScript is not enabled on the service and the printer cannot keep
up with the job rate. High-speed printers may happen to work if the PostScript attribute is not enabled,
simply because they finish the current job in the time it takes for the ETS to accept the next one.
2.12 Modem Features
The ETS supports both incoming and outgoing modem connections. The ETS can be configured to offer a
modem service to both LAT and Telnet users. Using the DSR and DTR signals from the serial lines (see the
Serial Pinouts appendix in your Installation Guide) the ETS ports can both log out an attached modem after
a connection exits and be logged out if the modem hangs up. Ports can also be configured to automatically
detect the baud rate at login time allowing multi-speed modems to connect easily.