Ethernet daisy chaining

May 28, 2007 2 Replies
A

I read this in Wikipedia near the end of the RMII docs:

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"Since the RMII standard neglected to stipulate that TX_EN should only be sampled on alternate clock cycles, it is not symmetric with CRS_DV and two RMII PHY devices cannot be connected back to back to form a repeater; this is possible, however, with the National DP83848 which supplies the decoded RX_DV as a supplemental signal in RMII mode [3]."



It seems to imply you can create a simple repeater with two PHY's "back to back" in MII mode. This would be useful for a new device we are working on that needs to daisy chain its Ethernet in and out. I can't find much info on how to do this, anyone done this and if so, how?



Thanks.


Allan Williams
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B

AFAIK it should be possible - from what I can tell that is what dumb ethernet hubs do anyway. See

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for a simple 3 port ethernet hub schematic.

Brendan Gillatt www.brendangillatt.co.uk GPG: 0x6E265E61
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A

Thanks for the input. Not sure that would apply to full duplex and 100 BT.

Looking at it further I think I've misread the wiki article - I think what they are referring to is a inline repeater used to double the segment length of a connection:

PC ---------------------- max length cable -------------------- [MII PHY - MII PHY] --------------------- max length cable ----------------------------- PC

This isn't what I need. What I want is my device to provide a repeater port for a local PC so it doesn't need its own LAN connection:

LAN ------------------------------------ my device ------------------------------ PC (PC sees the LAN through my device port)

I think I'll need to goto an Ethernet switch like the Micrel KS8993 unless someone has another idea how to do it discretely.

-- Allan Williams

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