C.4
Transparent Printer
The default device names to
Transparent Printer(TP) are /dev/lpXYY,
that is, the prefix name is changed from "tty" to "lp" but
the other "XYY" is the same. e.g. under default device names, the
corresponding TTY line of /dev/lpj11 is /dev/ttyj11.
By multiplexing a serial line, there are two sorts of
data channels
for TTY data(by /dev/ttyXYY) and TP data(by /dev/lpXYY). If the
/dev/ttyj11 is
used for a TTY, it has to be enabled before you would like to print
data
through /dev/lpj11 to a printer that connected to the terminal that is
operated
via /dev/ttyj11.
The channel for TP data that is uni-directional is used
to transmit
the data from a host to a terminal only. The differentiates of TTY data
and TP
data in the same serial line is that TP data are encapsulated within a
couple
of PRINT-ON and PRINT-OFF escape strings that are recognized by
connected
terminals. The PRINT-ON and PRINT-OFF is defined by connected terminals.
The scheme to
multiplex a serial line for these two channels is based on
time-division
method. The time slices for TTY or TP data are generated according to
the entry
procedure, polling, in the PCCOM driver, which is periodically called
by system
clock. The period of system clocks is different among various operating
systems, e.g. most UNIXs is 100hz, but SCO Xenix is 50hz.
The
interval reserved for TTY or TP channel in the same serial line is
important to
output TP data to a low-speed printer through high-throughput line from
PCCOM
cards if there is no flow control XON/XOFF to the serial line.
The
lpx command is used to adjust the time interval for TTY or TP data and
the TP
protocol.
¡Eoption:
-t number: set interval for TTY
-l
number: set interval for Transparent Printer
-n
string: set esc string to turn on printer
-f
string: set esc string to turn off printer
-T
: get interval for TTY
-L
: get interval for Transparent Printer
-N
: get esc_string to turn on printer
-F
: get esc_string to turn off printer
¡Edevice_name : lpXYY
The range of interval reserved for TTY or TP channel is
from 1 to maximum integer. The default setting for any /dev/lpXYY is as
follows:
Interval
for TTY : 50
Interval
for TP : 1
PRINT - ON escape :
¡§\033[5i¡¨ (ESC[5i)
PRINT
¡V OFF escape : ¡§\033[4i¡¨ (ECS[4i)
¡EThe examples to invoke lpx
1. Set 60 time slices reserved for
/dev/ttyj11
# lpx
-t 60
/dev/ttyj11
2. Set 2 time slices reserved
for /dev/lpj11
# lpx ¡V12 /dev/lpj11
3. Get the time slices reserved for /dev/lpj11
# lpx ¡VL
/dev/lpj11
4.
Set PRINT-ON string for /dev/lpj11
# lpx ¡Vn
¡§\033[51¡¨ /dev/lpj11
5. Get PRINT-OFF string
for /dev/lpj11
#
lpx ¡VF /dev/lpj11 \033[4i
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