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Re: parallel port

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  • mrjensan
    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 file/photo section?
    Message 1 of 8 , Aug 25, 2002
      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
      file/photo section?

      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?

      Thanks

      jen

      --- In Electronics_101@y..., "vijayxraju" <vijayxraju@s...> wrote:
      > Hi,
      >
      > 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
      source
      > about 6mA of current.
      >
      > It does provide some islation because the inputs are protected by
      > diodes.
      >
      > -Vijay
      >
      > --- 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
      > described
      > > above.
      > > > If the parallel communication lead is a long one, by the time
      > the
      > > signals
      > > > arrive at the other end they will have been degraded, and the
      > logic
      > > levels
      > > > can sometimes wander too far outside of their original TTL
      > levels,
      > > which
      > > > can lead to data corruption if this were to be mis-interpreted
      > by
      > > the
      > > > reciever. If you wanted to extend the cable length of a
      parallel
      > > 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
      > further
      > > length
      > > > of cable to be used.
      > >
      > > Hi Brain,
      > >
      > > Thanks. Does it also serve as an isolator for the PC from
      whatever
      > is
      > > on the other side.
      > >
      > > jen
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