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Re: 10base2 Ethernet bus architecture


ETRAX 100LX can be used with old style (SNI) 10 Mbit PHY circuits, e.g.
National Semiconductor DP8391A. How to connect it is described in the
Designer's Reference chapter 9.

The MCM includes an internal PHY, but it can be disabled, so it should be
possible to use an old style external PHY with the MCM too. This hasn't
been tested however.

These old style PHY circuits may be difficult to get nowadays. I don't
know which types that are still in production, but maybe someone else can
answer about that.

Also, I don't know how the software will react when it can't communicate
over the management interface. The old style PHYs don't have the
management interface. 

To make network boot work in SNI mode, you need to have a pull-down on the
MDIO pin on ETRAX 100LX. In the MCM, there is a 1.5 kOhm pull-up
internally on the MDIO, so there it may be difficult to use network boot
with the SNI type PHY. It is not advisable to connect the MDIO directly to
GND, since the SW may turn MDIO to an output.

Per Zander

On Fri, 19 Jul 2002, Claude Girerd wrote:

> Hi,
> For my application it would be very interesting if I could connect fewer ETRAX on 
> a bus architecture Ethernet network. The nodes will be close to each other and only 
> one node at a time will communicate on the network. 
> The 10base2 standard allows the use of an Ethernet bus architecture but which kind 
> of interface will I need to make this connection with an ETRAX or a MCM ?
> best regards,
> Claude
> _________________________________________________________________
> Claude GIRERD 
> Institut de Physique Nucleaire de Lyon
> 4, rue Enrico Fermi (Campus de la DOUA)
> 69622 Villeurbanne Cedex
> tel: 04 72 44 83 96
> fax: 04 72 43 14 52
> email: girerd@xxxxxxx.fr
> __________________________________________________________________