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Another method of Transparent Data Transmission is the Xerox defined SCS TRN
code 36. Generally accepted for use
in
laser printer applications, this method is
the same as the Coax Interface non-translate method above. Control code
sequence rules are the same for SCS code 36 as for code 35.
ALTERNATE HOST (PC) AUTO PARALLEL SHARING
If the C82314* is connected to a PC with
the parallel sharing cable, the PC
must be turned on.
The coax interface card has a mini-Centronics parallel connector which enables
it to automatically share the printer between the 3270 host and the alternate host
(usually a personal computer). The interface periodically checks the 3270 host
and the PC until it finds input data to be printed. The interface continues to print
using data from the current source until the input data stops and no additional
data is received for the period of time specified with Commands 50 or 51.
(Factory defaults are 5 seconds for the parallel port and 10 seconds for the 3270
port.) The other source is then checked for the presence of data to be printed.
The automatic checking for data from either sources is accomplished constantly
when both hosts are idle. The host with the first data will have printing priority
until it has printed all of its data and remained idle for the time interval specified
in Commands 50 or 51.
The Epson printer may have large print buffers, so an actual physical break in
printing may not be seen between print jobs, yet the interface pauses for the
specified time period without passing data to the printer before changing to the
other port. While the 3270 host is active, the parallel port accepts the first parallel
byte and then goes busy. This allows the interface to know that parallel data is
waiting. Conversely, while the parallel port is printing, the 3270 coax port will
receive data and then send a busy signal to the host until the printer is available
(the time-out period on the parallel port has expired with no additional data having
been received). PC printing longer than 20 minutes may cause the 3270 host to
drop communication with the printer.
Prior to printing a coax host document, if the previous document comes from the
PC sharing port, the interface card sends the coax port initialization string to the
printer and restores the printer’s format that was fast specified by the coax host
when switching to coax printing (see Appendix A, Command 57). Also, before
printing an initial document from the PC Share port, the interface sends the user
defined shared port initialization string (see Appendix A Command 56). The
alternate (PC) host must send the printer all of the necessary formatting
instructions and commands
for
correct printing.