Re: Parallel port device

Bradley D. LaRonde (brad@ltc.com)
Thu, 19 Aug 1999 08:56:18 -0400


> I am building some hardware to allow my computer to control a mains
> appliance, and was planning to have the parallel port drive an
opto-isolated
> relay. However, it occured to me that maybe it isn't possible to hold a
bit
> on the parallel port high for an arbitrarily long time. If so I'd need to
> put some kind of bistable circuit into my hardware.
> Can anyone tell me whether this is the case or not?
>
> Thanks,

I think that you can hold the bits high on the parallel port (not sure about
that), but maybe not through the existing parport driver (also not sure).

However, FWIW, putting a latch in your hardware might be the way to go
anyway. That way you could probably use the regular parport driver to
output a byte, and if your computer goes off, your device can keep its
state. You device would be more like a normal parallel port device and
respond to the strobe signal to latch the bits from the parallel port into
itself.

Regards,
Brad

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