Re: parallel port
- Hi Vijay,
Sorry for being electronically dense, (but still want to fiddle) how
do you use the 74HC244? Is there a schematics in the group's
Say we want to feed signal from pin 2 and pin 3 from parallel port.
Where do we feed the wires onto the 74HC244 and from which pins on
the 74HC244 do we take the output?
--- In Electronics_101@y..., "vijayxraju" <vijayxraju@s...> wrote:
> All parallel port pins have a 10K pull up internally. So @5V they
> will give u not more than 0.5mA. SO if u are thinking of drawing
> power from the parallel port DON'T, u may burn it!!!!
> A parallel buffer is a chip that is used to overcome this current
> sourcing problem. I nnormally use a 74HC244
> (http://www.solarbotics.net/library/datasheets/74HC244.pdf) for my
> applications. Its an octal (8 lines) 3 state buffer which can
> about 6mA of current.
> It does provide some islation because the inputs are protected by
> --- In Electronics_101@y..., "mrjensan" <jensan@s...> wrote:
> > --- In Electronics_101@y..., "BrianJHoskins" <BrianJHoskins@u...
> > > > > What is a parallel buffer?
> > >
> > > A parallel buffer would help alleviate the very problem
> > above.
> > > If the parallel communication lead is a long one, by the time
> > signals
> > > arrive at the other end they will have been degraded, and the
> > levels
> > > can sometimes wander too far outside of their original TTL
> > which
> > > can lead to data corruption if this were to be mis-interpreted
> > the
> > > reciever. If you wanted to extend the cable length of a
> > type
> > > communication link, then you would need a "buffer" in between,
> > which would
> > > re-condition the degraded signals, bringing them back to their
> > original
> > > accurate TTL levels and sending them back out, allowing a
> > length
> > > of cable to be used.
> > Hi Brain,
> > Thanks. Does it also serve as an isolator for the PC from
> > on the other side.
> > jen