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.