Operations Manual
PCCOM PCI 8 port universal RS232 card
DECISION Computer International
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To change baud rate, please update /etc/inittab and
/etc/conf/cf.d/init.base files.
C.3 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-
