Re: [PARPORT] Two or more interrupt-driven devices?

Matthias Jim Knopf (
Sat, 13 Mar 1999 16:14:58 +0100 (MET)


> > > So according to this, maybe I have to connect each button both to the
> > > pin that can generate interrupt and another which can be read as info
> > > of which button is pressed. Thus I have to make a complex structure of
> > > outside buttons(maybe I have to set up some gates avoiding their
> > > interference).
> > >
> > > I wonder whether whether there's a much easier structure.
> Here's the simplest control I can think of: You use the high and low
> signals from the cable (sorry I forget the pin #s, no book)
btw: everbody who wants to have a short gziped (7k) documentation
about all sort of computer-connectors (from Power-Connector to SCSI)
sould write me an email!

> and use those as +V and GND for your gates.
Unfortunately there is no +V line, but what you might have thought of
is using a pin as +V, that be can rised constantely, such as a
data-pin or pin #14 "Auto Feed"...

> Get up to 4 debounced buttons. Each should
> have 3 connection pins: GND, +V, output. Connect the GND and +V pins to
> the apropriate wires from the parport. Connect the output pin to one of
> the parport input line. Line 10 should be connected an or gate (or
> rather equivalent made up of nands) whose inputs are the outputs of the
> switches.
ok, I understand the NAND-version, but what again was the other

> If I am understanding you correctly, we call those debounced buttons.
> They have 2 outputs to an rs flip-flop, the output of which you read. The
Right! That's just the thing I thought of! ;-)

> design of the switch plus the attached flip-flop "eats" all the bouncing
> between connected and disconnected, so that the signal goes cleanly from
> low to high. I'm almost certain that's what you're talking about.
You're right! :))

So far, Jim (Matthias Knopf)

No RISC, No Fun           PGP-Key available
Murphy was an optimist

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