How does lpr know printer is offline?

[Bill Daniels]

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.

We are really trying to avoid a situation in which the printer is placed
offline while the spooler is inactive and a print job queued while the printer
is still offline.  In this case the spooler goes merrily about its way of 
dumping a bunch of stuff to the printer which isn't expecting it, doesn't
know that it has started, and consequently loses the job.

We also have available DECserver 200/MC ports across LAT if that will help
with a solution.
-- 
bill daniels
federal express, memphis, tn
{hplabs!csun,mit-eddie!premise}!fedeva!wrd3156