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SubjectOfftopic: Re: DE and hot-swap disk caddies

On Thu, 28 Mar 2002, Alan Cox wrote:

> > Then there is this talking around about the "tristate of some" device.
> > I'm really a bit sick of it. Becouse there is no such a state
> > like a tri-state. We have just bus drivers on both ends.
> > They are implemented usually as Schmidt triggers. They have three
> > possible states on output: low voltage, high voltage, high resistance.
>
> Which is one, two, three states -> tri-state.

Eeks, a Linux developper who can count ;-)

> Electronics terminology then abuses that to mean the high impedance state (not
> high resistance please if we are going to be picky).

Correct, though I hope in most cases the impedance is almost equal to the
resistance, otherwise there would be problems at the current high speeds.

For those who don't know the difference:

Resistance is only a part of impedance. Inpedance also contains a
frequency-dependant part, caused by induction in, and capacity between
wires and electronic devices.

The idea in formula:

Induction = Resistance +
frequency * Induction +
1 / (frequency * Capacity)

For an accurate formula, see any book about EE.

Jos

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