How does lpr know printer is offline?

[George Robbins]

In article <463 at fedeva.UUCP> bill at fedeva.UUCP (Bill Daniels) writes:
> We have a Printronix P300 serial printer connected to an Ultrix MicroVAX
> 3800 via a CXY08 8-line RS232 controller.  Which of the RS232 signals
> is monitored by the lpr print spooler to recognize that the printer is
> off-line?  The printer can be configured to drop either CTS or DTR.
> The printer can also send an XOFF (dc1/^S) but this seems to be ineffective
> if the spooler is not in active communications with the printer; I guess
> nothing has the port open for read at the time in order to pick up the
> software flow control character.

"offline" is relative in this case.  If you have the serial port configured
for modem control (flags in config file and possible mode bits in the
/etc/printcap file) then you should be able to use the "drop CTS" option
to effect a form of hardware flow control.  You might also be able to
cross-wire the printers "DTR" line to your "DSR" and/or "CD" line which
would make attempts to "open" the printer hang/fail while it is offline.

None of this is really printer specific, it's just taking advangage of
some of the stuff supported by (some of) the serial drivers/interfaces.
If you enable "modem control", you generally need to connect DSR, CD, and
possible CTS to some signals to make sure they are "asserted" as if there
were really a modem attached.

-- 
George Robbins - now working for,	uucp: {uunet|pyramid|rutgers}!cbmvax!grr
but no way officially representing	arpa: cbmvax!grr at uunet.uu.net
Commodore, Engineering Department	fone: 215-431-9255 (only by moonlite)