Parallel Port Interface / correction!

Correction! Not a NAND (lost my mind apparently),
we need an EXCLUSIVE-OR gate as Alan suggests.

But the '136 is not a SCHMITT trigger either..

So here is an alternative (I can't remember the
chip I used last time, can't find my book...),
so the suggestion instead is a:

Non-Inverted:
- 74'341 or 74'344 octal buffer/line driver with Schmitt
trigger

Inverting:
- 74'340 octal buffer/line driver with Schmitt trigger

Both have the same pinouts, so if you use a socket, you
can just switch chips to change between inverting and non-inverting.
All three devices are 3 state, but we will just enable them
permanently (using pin1 and pin19).

Bonus points to Alan for keeping me honest....

- - - - - -

Alan Marconett KM6VV wrote:

>
> Hi Doug,
>
> the '132 is a NAND, but I think you're confusing it. Gnd a NAND input,
> and you get nothing through. Tie an input HI, and the signal goes
> through INVERTED. Now a '136 is an EXCLUSIVE-OR gate, and work similar
> to what you're saying. Perhaps that's the one you're thinking of?


> Doug Fortune wrote erroneously under the influence of

insufficiently caffeinated coffee:

> >
> > I think I suggested this idea before (using single ended signals,
> > buffering them to higher strength, and using a Schmitt trigger
> > type device (with built in hysteresis):
> >
> > Using a 74LS132 quad 2-input positive NAND Schmitt trigger TTL
> > chip (under a buck), you can use it this way:
> >
> > As it is a NAND, if you hook one input up to GND and the other
> > input to your signal (and I am presuming this chip is right next
> > to the encoder, for buffering the signal down to your driver/PS
> > box), then you get:
> > - the buffering
> > - Schmitt trigger hysteresis (good for noise reduction)
> > - the signal is NOT INVERTED.
> >
> > However, if you do want the signal inverted (to fix the problem
> > above where EMC, or some other program, doesn't like it some
> > particular way) hook one input up to +5, and the other input to
> > your signal, then you get:
> > - the buffering
> > - Schmitt trigger functionality
> > - the signal is INVERTED.
> >
> > In fact, since the chip has 4 NAND circuits, you can hook a
> > circuit up both ways when you originally solder it together,
> > and select what you want (Inverted or Not Inverted) to suit
> > the circumstances.
> >
> > Doug Fortune
> > http://www.cncKITS.com
>
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