Ethernet TTL Direct Connection

[ricko_uk]

Hi,
is it possible to connect 2 micros on the same board to each other using Ethernet connection?
Obviously placed only few mm apart from each other and obviously using matched length/impedances traces.

If so then anything should I be aware or careful about in the design?

Thank you

[donotdespisethesnake]

By "Ethernet TTL"  I guess you mean MAC to MAC, rather than PHY to PHY. I believe MAC connection is possible with a RGMII interfaces, can't say I've ever seen it done though.

[T3sl4co1l]

AFAIK, yes, you just need to swap the RX/TX lines much as you'd connect a UART.  I haven't done it but I've ran across a few appnotes that seem to cover it.

Tim

[David Hess]

It is definitely feasible.  Between boards or chassis where there may be a ground difference, the signals can be AC coupled.

[T3sl4co1l]

It is definitely feasible.  Between boards or chassis where there may be a ground difference, the signals can be AC coupled.

Do you mean MDI?  Yes, that works, just use pullup resistors and coupling caps, no transformers needed -- or just the one transformer for better isolation than capacitors.  (To clarify, coupling capacitors alone, works for small ground-to-ground offsets: maybe fractional volts at AC, up to say tens of volts at DC.  Whereas the transformer gives very low isolation capacitance, allowing much more freedom at both AC and DC.)

For MII, I don't know that it can be AC coupled?

Tim

[David Hess]

It is definitely feasible.  Between boards or chassis where there may be a ground difference, the signals can be AC coupled.

Do you mean MDI?  Yes, that works, just use pullup resistors and coupling caps, no transformers needed -- or just the one transformer for better isolation than capacitors.  (To clarify, coupling capacitors alone, works for small ground-to-ground offsets: maybe fractional volts at AC, up to say tens of volts at DC.  Whereas the transformer gives very low isolation capacitance, allowing much more freedom at both AC and DC.)

For MII, I don't know that it can be AC coupled?

I mean for MDI and there are application notes discussing it.