Ethernet daisy chaining

I read this in Wikipedia near the end of the RMII docs:
http://en.wikipedia.org/wiki/RMII

"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

On Mon, 28 May 2007 21:27:36 GMT, "Al Williams"
<donotreplydirect@usenewsgroup.com> wrote:

>I read this in Wikipedia near the end of the RMII docs:
>http://en.wikipedia.org/wiki/RMII
>
>"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.

AFAIK it should be possible - from what I can tell that is what dumb
ethernet hubs do anyway.
See http://www.zen22142.zen.co.uk/Circuits/Interface/pethhub.htm for a
simple 3 port ethernet hub schematic.
-- 
Brendan Gillatt
www.brendangillatt.co.uk
GPG: 0x6E265E61

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



"Brendan Gillatt" <brendan@brendanREMOVETHISgillatt.co.uk> wrote in message 
news:cslm53l8kca7mcta2fa6scbm2cblp7mql4@4ax.com...
> On Mon, 28 May 2007 21:27:36 GMT, "Al Williams"
> <donotreplydirect@usenewsgroup.com> wrote:
>
>>I read this in Wikipedia near the end of the RMII docs:
>>http://en.wikipedia.org/wiki/RMII
>>
>>"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.
>
> AFAIK it should be possible - from what I can tell that is what dumb
> ethernet hubs do anyway.
> See http://www.zen22142.zen.co.uk/Circuits/Interface/pethhub.htm for a
> simple 3 port ethernet hub schematic.
> -- 
> Brendan Gillatt
> www.brendangillatt.co.uk
> GPG: 0x6E265E61