Hi, people!

I'm new to mbed and I have to use it to communicate with another microcontroller. Well, I'd want to know if the hardware connection may be direct - I mean, a "crossover" connection - between the mbed and the other microcontroller, not needing magnetics or related stuff.

Thanks a lot!

Diego,

Connecting the Ethernet ports between two controllers without isolation will probably not work. Ethernet PHYs have various ways of biasing themselves and the biasing of one brand of Phy will be different from another brand. The end result will be frustration. You will need at least one transformer and terminating resistors on both ends.

...kevin

Hi, Kevin! Thank you for the reply!

What about capacitive coupling? Can it replace the use of magnetics in such a case?

Thank you again!

Maybe Diego,

Again, it depends on the Ethernet Phy's you are interfacing to and that they get biased correctly. I had successfully done this once in my carrier. I'm 1 for 1.

...kevin

Diego,

See National Semiconductor's application note AN1519 "DP83848 PHYTER® Transformerless Ethernet Operation". http://www.datasheetarchive.com/3--DP83848%2F49-datasheet.html

You will need

1. (4x) 50 ohm terminating resistors
2. (2x) 100 nf by-pass capacitors, and
3. (4x) 33 to 100 nf coupling capacitors (as 2 matched pairs?).

Items 1 and 2 are already on the mbed. A cross-over connection should be no problem. If the other (non-mbed?) micro does not have magnetics, it may have it's own terminating and bias requirements.

There are caveats in the application notes on cable length and 10 base T vs 100 base T modes.

Fred