Open Drain or Tri-state???

What are some rules of thumb for using open drain vs. tri-state
outputs?

I am interfacing to a PowerPC 8280, and found some note that TA has to
be
actively negated and then tri-stated. Why is that?

If I use an open drain output, is it better to code it as such (i.e. a
<= '0' when (condition) else 'z', or should I just code it as if it
were an active signal (i.e. a <= b and set the pin to open drain in
the vendor software?

Analog Guy

"Analog Guy" <> wrote in message
news: om...
> What are some rules of thumb for using open drain vs. tri-state
> outputs?
>
> I am interfacing to a PowerPC 8280, and found some note that TA has to
> be
> actively negated and then tri-stated. Why is that?

To place charge on the line to hold it.

> If I use an open drain output, is it better to code it as such (i.e. a
> <= '0' when (condition) else 'z', or should I just code it as if it
> were an active signal (i.e. a <= b and set the pin to open drain in
> the vendor software?

Think about that.

fabbl