Perle Systems Adaptors What is transparent printing?

UltraPort Serial Adaptors User Guide
Page 130
What is transparent printing?
Most terminals have an auxiliary (AUX) port which can be connected to a serial printer. Data
can then be output to the terminal or the printer via the same serial line. This is called
transparent print (or xprint) and is designed for printing simple ASCII text. A separate xprint
device node (ttyznp where n is device number) is created for each port. This device is
enabled automatically if either the local or modem device is enabled for the port.
When a host card receives data addressed to the transparent print device it prefixes it with
the transparent print mode ON string and appends it with the transparent mode OFF string.
The ON and OFF strings for each terminal type available are defined by the printcap.spd
file. See The printcap.spd configuration file on page 131 for more details.
When the host card receives data addressed to the transparent print device, it prefixes it with
the Transparent Print Mode ON string and appends it with the Transparent Print Mode OFF
string. Terminal I/O has absolute priority over printer output. Transparent print data will only
be sent when there is a break in output to the terminal (for more than a tenth of a second)
For each port, the transparent printing parameters are controlled by an entry in the print.spd
file found in the /etc/ directory on your system. The entry for each port includes definitions of
the terminal type, transparent print throughput rate and device name. See The print.spd
configuration file on page 132 for further details.
Serial communications
port on terminal
Terminal
Auxiliary port
on terminal
Printer
SPEED Port
Configuration utility
print.spd file
SPEED Device
driver
UltraPort host
card
SCO OpenServer
operating system
Computer system