When you say that the lines are "open" or "closed", what exactly do you
mean. If by open you mean not connected, and by closed you mean
connected to ground, then that could be the source of your problem. You
should be connecting the lines to 0V or to +5V to generate signals (you
could get the +5V from one of the output lines of the port if you want).
When you leave the line disconnected (open) you could get a variety of
strange behaviors depending on your exact hardware implementation.
Quoted from Damien Mattei on Tue, May 06, 2003 at 09:45:48AM +0200.
> i wrote a litte soft for monitoring alarms connected to // port under
> linux.( see: http://www-iag.unice.fr/guardian/guardian.html )
> it's a system quite simple if the circuit on one of the 5 lines (BUSY,
> PAPER OUT, SELECT, AUTOFEED, ERROR) is open the data read is true and
> false if it is closed.It worked well during one year, but now the data
> are always read as false, so if an alarm occured it will not be
> monitored as before. The problem is that it happens randomly ,on any
> lines, and randomly after a period of time,when it happens it is not
> reversible until i reboot the system with no power off needed.
> So the linux kernel (or the BIOS?) seems to be able to do a soft reset
> on the // port at boot time, if i can do this reset in my own program
> the system will work again but i can't find on the internet how to do
> this , perheaps someone in the mailing list know that or have an advice?
> best regards
> Damien MATTEI
> C.N.R.S - UMR 6549 - U.N.S.A
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