I have what I think is a strange problem, and I just can't figure it
out. Hopefully somebody here can help me.
I have essentially eight LEDs connected to the data lines of my parallel
port. On my windows PC at work I have software that allows me use the
parallel port as a digital I/O device. When I plug my LEDs into the
parallel port on that computer I can turn on or off any LED as I please.
When I plug the LEDs into my the parallel port of my Linux box I see the
strange behavior. Some of the lines are active intermittently. D0 is
modulated with a very high duty cycle. Lines 3,4 and 7 seem to be high
all the time, and lines 1 and 2 pulse about ten times a second. Several
of the lines flicker whenever there is a hard drive access. Near as I
can tell, the lines are a reflection of the interrupt status of the PC.
If I write data out on the lines, the LEDs show it, but the data is
immediately "erased." If I put the program into a tight loop, the lines
will reflect the data I am trying to write (i.e.
for(;;){ioctl(fd,PPWDATA,0)} will turn off all of the lines).
If I do 'cat file.txt > /dev/lp0' the LEDs go out, but still flicker
like they are being turned on and immediately turned off by the lp
driver.
I know the parallel port works because I had a printer connected to it
until recently.
Is my description clear? Any thoughts?
Thanks,
Dave
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This archive was generated by hypermail 2b29 : Thu Mar 14 2002 - 22:16:34 EST