Re: [CAD_CAM_EDM_DRO] Parallel Port/Relay Problems... more

Hi Chris, Matt,

Actually, they can be tri-stated (floated, high impedance). They will
not be inputs unless they are bi-directional buffers.

To expand just a little, there are also open-collector buffers, which
are meant to work into a load with a pullup. They only sink current.

Alan KM6VV


ccs@... wrote:

>
> > Typical tri-sate output stages of buffers used for parallel ports can
> > either pull a line up (source) or down (sink).
>
> Actually, if they are TRI-STATE buffers there is a third option - they
> can be configured as inputs. In this case they will present a small
> load - although if CMOS the load will only be seen when the signal is
> switching, as these inputs draw no steady state current.
>
> Chris Stratton