[clue-tech] making ethernet autonegotiation not work

[Jim Ockers]

Hi Warren,

> > >Right, I should have mentioned that we have some very specific
> > >environmental requirements and the "industrial" ethernet equipment
> > >that meets the temperature/power/static/corrosion/hazardous location
> > >requirements is expensive.  We can't use normal consumer grade gear.
> > 
> > And the unmanaged $50 switch gives you all of the above?
> 
> Okay. So drop the 100MBps device and replace it with a ~$50 10BaseT
> device. At [1], you'll find a 10BaseT Hub that conforms to the 802.3
> inducstrial standard. Does that meet your needs? If the hubs won't
> support 100MBps, it shouldn't be able to negotiate the higher speed.

That's along the right lines, thanks for the suggestion.  The thing is,
we need to use a switch, not a hub, so that the signal gets cleaned up
when the frames are copied to the other port(s).

We have been unable to find any unmanaged 10BaseT switches.  Also our
selection of vendors is limited to those who make devices of a certain
size with DIN rail mounts so we can mount them in our hazardous location
enclosures.

Basically we have ruled out trying to solve this problem with different
NICs (the link partners are industrial single board computers with
built-on onboard network interfaces), hubs (because we need the switch
signal processing), and software configuration on the link partners
(already tried that).  Changing the cabling and connectors is not an
option - that's what's driving this whole investigation.

I had a look at the Altex site and didn't see any switches that were
10BaseT only.  I know it used to be possible to buy only 10BaseT
switches but they were big rack mount things.  It's been a long time
(>5 years) since I've seen a switch that was 10BaseT only.  The 3Com
switch 1100 comes to mind.

Basically the only thing I can think of that would make the ethernet
autonegotiation not work is to somehow defeat the link pulses so
that everything falls back to 10BaseT half duplex, the lowest common
denominator.

However I don't think that's possible either, so we might have to go
with the $500 managed switch and set the ports to 10BaseT only.  (And
hope that it doesn't "forget" its settings when it takes a lightning
strike or some other bad power event.)

Thanks everyone for your suggestions,
Jim

-- 
Jim Ockers, P.Eng. (ockers at ockers.net)
Contact info: please see http://www.ockers.net/