Em 6/9/2011 08:55, Forrest Christian escreveu:
> I have a new board, my first using the 18f67J60 'EtherPIC'.
>
> In the process of designing this, I needed magnetics which are capable=20
> of Extended Temperature range - and I found seemingly compatible (and=20
> easily obtainable) magnetics from EPCOS.  =20
> (http://www.epcos.com/inf/30/ds/lan_mod/B78476A8247A003.pdf )
>
> So tonight was the first attempt at getting firmware on the board, and=20
> everything working.   After tweaking on the Microchip TCP/IP stack (to=20
> eliminate a lot of crap related to their samples), I got some sample=20
> code loaded, and verified working, EXCEPT I couldn't get an ethernet link=
..
>
> Eliminating a lot of a long story of a few hours of troubleshooting, I=20
> finally decided to try removing the magnetics from the board and=20
> operating 'magneticless' - or more accurately rely on the magnetics in=20
> the ethernet switch to do the isolation - amazingly it linked first try.
>
> So obviously there was something weird with these magnetics.  I don't=20
> have a spare where I am right now but I sure can't see anything=20
> mechanically wrong with them (and electrically they seem ok - at least=20
> as much as you can tell with a voltmeter).
>
> I've been through the datasheets and compared specs and requirements,=20
> and pinouts, about a thousand times (ok, an exxageration, but it sure=20
> feels like it).
>
> So the question being:  Can anyone see something I missed as far as the=20
> specs on these magnetics which would make them *not* work with the 67J60?
>
> -forrest


It is important to use the correct turn-ratios, usually 1:1CT+1:1CT for
the PIC18F67J60.
There are other important parameters for the transformer also, such as
inductance and leakage inductance.

Also the value of the Rbias resistor and of the other external passive
components connected to the transformer are critical and must be 1%
tolerance, except capacitors.


Isaac

--=20
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