Hi Colin,
On 23 October 2011 13:48, Colin Law <[email protected]> wrote:
> I think the capacitance might
> be the problem rounding off the signals, but I don't know enough about
> the physics to know the answer. I am sure it would work over a
> "short" distance but not over a "long" distance. The question is what
> are short and long in this context?
>
> I am not sure that the ethernet over coax point is valid as I assume
> the drivers in such an interface would be designed to drive coax.
>
That was my point - pure resistance isn't going to be the issue. Signal
quality is - hence the reference to 100mbps ethernet. If it is possible to
have coax ethernet for 500m, compared with twisted pair ethernet for 100m,
then I would have thought that similar principles apply to 1-wire. However,
with coax ethernet, signal reflections become an issue, and it is important
to use a terminating resistor or active termination (which also applies in
I2C iirc).
So, what we need if for someone knowledgeable in digital circuit design to
chime in. What is the theoretical maximal distance we could achieve here?
Would a standard 75Ohm termination suffice, or might it be worth designing
something better? And, while I am thinking about it, can I design my network
as a 'T' topology?
Cheers,
Phil
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