NetWare 4.1/9000 Print Services

A-15
Setting Up and Servicing Printers
Troubleshooting Printers
Serial Communications Channel
Serial (RS-232) communication channels usually depend on certain control
codes, such as X-On/X-Off, being sent as part of the data stream. A
PostScript job on an RS-232 channel may include additional control
characters to perform these tasks:
• Request printer status (0x14)
• Interrupt the PostScript interpreter (0x3)
• Signal the end of a job (0x4)
Other control codes may also appear, such as 0x1, 0x11, 0x13, and 0x16,
which perform similar functions.
When a serial printer receives a data stream containing control codes, the
printer’s communications interface traps and removes the control codes.
When this is the case, it means that the serial channel is not binary-capable.
If you direct binary data to this type of communication interface, some data
values will be misinterpreted as control characters and erroneously stripped
out. This, obviously, will affect the printer output, and cause distorted or
garbled printing.
Also, a serial channel may be configured to use less than 8 bits of data per
character, as described in the next section.
Parallel or Hewlett-Packard Remote Printer Communications
Channel
Centronics Parallel and Hewlett-Packard Remote Printer communications
channels use 0x4 (Control-D) to signal the end of a job to the PostScript
interpreter, or 0x3 (Control-C) to interrupt the interpreter, primarily because
of the precedent set by the serial channel. This means that parallel and
Remote Printer connections are also not binary capable.
DOS PostScript Applications Generating Control-D
Many DOS and Windows applications generate PostScript to be sent to a
printer across a serial or parallel interface. These applications include the
Control-D (0x4) character to signal the end of the job. If this data is sent to a
queue serviced by an AppleTalk printer, the Control-D character will be