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Forum: µC & Digital Electronics Ethernet cross 1:1


Author: Dirk (Guest)
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I use ethernet with an AVR32. Connected to a switch with a 1:1 cabel and 
direct to a network-card with a cross-over cabel. Is it possible to 
connect two RJ45, wired 1:1 and cross-over, to a single MAC?
Of course only one connection can be used at a time, but whatever cable 
you have you can connect to whatever port, switch/hub or netword-card.
Does the unused port must be terminated in some way?

Many thanks for your help

Author: Schrotty (Guest)
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>Is it possible to
>connect two RJ45, wired 1:1 and cross-over, to a single MAC?
No! You cannot connect a RJ45-Jack or Cabel to a MAC. You can connect it 
to a PHY which is connected to a MAC.

Modern ethernet PHY´s support auto-X-over functionality, which 
automatically detects, whether a crossed oder a straight cable is 
connected.

Author: Dirk (Guest)
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Thanks for your help.

The phy on my board do not auto-detect the wiring. Only modern 
GigE-cards must have this feature. Old 100Mbit cards do not. OK, if I 
wire two RJ45 with magnetics to my single phy, does the unused wires 
will disturb the wires used? Both RJ45-connectors are still connected to 
the single phy. Do I have to terminate the unused RJ45-connector?
It is only for the convenience of the user. Whatever cable he have and 
to whatever he want to connect the uC, choosing the correct 
RJ45-connector and done.

Author: Schrotty (Guest)
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A lot of 100MBit PHYs support auto-x-over! but it´s not a "must", that´s 
true..

You want to attach TWO magnetics and Jacks to ONE PHY?????
That´s (sorry) crap!

If you design your own PCB why don´t you use a simple 100MBit PHY with 
auto-x-over and one Jack
(e.g. 
http://www.micrel.com/page.do?page=product-info/fa... )

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