Simple tests of an Ethernet port?

I am charged with a holy crusade of debugging a 100bT Ethernet
interface of unknown functionality, and the information I've been
given suggests that there is an analog problem in the media interface.

Can someone point me to any kind of preliminary tests I can perform to
determine "out-of-specedness" using standard lab tools; scope, DMM,
etc? Googling leads me to lots of hellishly expensive dedicated
Ethernet testers, of course...

I've exhausted everything I can think of on the software end.

"Lewin A.R.W. Edwards" <larwe@larwe.com> wrote in message
news:608b6569.0404211459.52fdc85@posting.google.com...
> I am charged with a holy crusade of debugging a 100bT Ethernet
> interface of unknown functionality, and the information I've been
> given suggests that there is an analog problem in the media interface.
>
> Can someone point me to any kind of preliminary tests I can perform to
> determine "out-of-specedness" using standard lab tools; scope, DMM,
> etc? Googling leads me to lots of hellishly expensive dedicated
> Ethernet testers, of course...
>
> I've exhausted everything I can think of on the software end.

Scope the signals. It's easier on the interface chip side
of the magnetics. If you have nothing connected (switch,
hub), terminate the signals with 100 - 150 ohms each.

IIRC, the SMSC LAN91C111 manual has the signal form specs.

A 100BASE-TX chip should be sending the negotiation pulses
when starting up. The pulses are extended versions of
10BASE-T link pulses (called FLP, Fast Link Pulses),
10 Mbits/s data pulses.

The 100BASE-TX data stream is a continuous string of
125 Mbit/s data, due to the 4-to-5 encoding.

HTH

Tauno Voipio
tauno voipio @ iki fi

Lewin A.R.W. Edwards wrote:

> I am charged with a holy crusade of debugging a 100bT Ethernet
> interface of unknown functionality, and the information I've been
> given suggests that there is an analog problem in the media interface.
> 
> Can someone point me to any kind of preliminary tests I can perform to
> determine "out-of-specedness" using standard lab tools; scope, DMM,
> etc? Googling leads me to lots of hellishly expensive dedicated
> Ethernet testers, of course...
> 
> I've exhausted everything I can think of on the software end.

First ping its owm
Then ping something else and measure the signals.

Rene
-- 
Ing.Buero R.Tschaggelar - http://www.ibrtses.com
& commercial newsgroups - http://www.talkto.net

larwe@larwe.com (Lewin A.R.W. Edwards) wrote in message news:<608b6569.0404211459.52fdc85@posting.google.com>...
> I am charged with a holy crusade of debugging a 100bT Ethernet
> interface of unknown functionality, and the information I've been
> given suggests that there is an analog problem in the media interface.
> 
> Can someone point me to any kind of preliminary tests I can perform to
> determine "out-of-specedness" using standard lab tools; scope, DMM,
> etc? Googling leads me to lots of hellishly expensive dedicated
> Ethernet testers, of course...
> 
> I've exhausted everything I can think of on the software end.

The answer to yout post is in your post:

"there is an analog problem in the media interface"

"standard lab tools; scope"

"out-of-specedness"

"exhausted everything on the software end"

Thus:

1) get a copy of the analog specifications of the signal

2) use a standard scope (differential probing) with adequate bandwidth

3) get the hardware guy to investigate

Then you see the waveforms of the frames and you can check whether they comply.


- Thierry Moreau

CONNOTECH Experts-conseils inc.

See the PPCMB/850 embedded processor module
and the ABCD Proto-Kernel(tm) at

web site: http://www.connotech.com
e-mail: thierry.moreau@connotech.com

Lewin A.R.W. Edwards wrote:
> I am charged with a holy crusade of debugging a 100bT Ethernet
> interface of unknown functionality, and the information I've been
> given suggests that there is an analog problem in the media interface.
> 
> Can someone point me to any kind of preliminary tests I can perform to
> determine "out-of-specedness" using standard lab tools; scope, DMM,
> etc? Googling leads me to lots of hellishly expensive dedicated
> Ethernet testers, 

RENT the expensive tester.  You will learn more with it faster than
any other way I can think of, except hiring an MIT professor :-)

Hi Tauno,

> > Can someone point me to any kind of preliminary tests I can perform to
> > determine "out-of-specedness" using standard lab tools; scope, DMM,
> 
> Scope the signals. It's easier on the interface chip side

I'll download that datasheet, but the problem I am _suspecting_ is
that the connector (which has integral magnetics) was chosen randomly
and isn't matched correctly to the rest of the circuit. I am still
waiting for a datasheet for the part. I'm thinking of _really_ basic
tests here, btw - signal amplitude, impedance of the output
transformer

"Lewin A.R.W. Edwards" <larwe@larwe.com> wrote in message
news:608b6569.0404221831.30f94c92@posting.google.com...
> Hi Tauno,
>
> > > Can someone point me to any kind of preliminary tests I can perform to
> > > determine "out-of-specedness" using standard lab tools; scope, DMM,
> >
> > Scope the signals. It's easier on the interface chip side
>
> I'll download that datasheet, but the problem I am _suspecting_ is
> that the connector (which has integral magnetics) was chosen randomly
> and isn't matched correctly to the rest of the circuit. I am still
> waiting for a datasheet for the part. I'm thinking of _really_ basic
> tests here, btw - signal amplitude, impedance of the output
> transformer

The impedance shown on the twisted pair should be 100 or 150 ohms,
depending on the cable type: STP or UTP. In practice, small
reflections do not harm, so as a compromise, you could start
with 120 ohms.

It is difficult to produce twisted pair cable with impedance
outside of the range, due to the inverse logarithmic relation
of the wave impedance and cable diameter/spacing ratio.

The signal on the line should be in the range of 600 mV with
the proper impedance. The transformation ratio of the magnetics
unit and the terminating resistors must be selected to match
both the signal amplitude and impedance conditions. The typical
ratios are from 1:1 to 2:1.

Admitted, the signal is RF, but the wavelength (even at the
third harmonic, 188 MHz) is well over a meter (little over a
yard, for the foot-pound people), so a couple of millimeters is
nothing.

HTH

Tauno Voipio
tauno voipio @ iki fi

Tauno Voipio wrote:
...> Admitted, the signal is RF, but the wavelength (even at the
> third harmonic, 188 MHz) is well over a meter (little over a
> yard, for the foot-pound people), so a couple of millimeters is
> nothing.

That reminds me of a common error when people wire up their own 
ethernet routers: they use as short a cable as reasonable, but they 
should never use less than a couple of meters single length, right?

"Rick Merrill" <RickMerrill@comTHROW.net> schrieb im Newsbeitrag
news:JV8ic.10862$aQ6.875998@attbi_s51...
> Tauno Voipio wrote:
> ...> Admitted, the signal is RF, but the wavelength (even at the
> > third harmonic, 188 MHz) is well over a meter (little over a
> > yard, for the foot-pound people), so a couple of millimeters is
> > nothing.
>
> That reminds me of a common error when people wire up their own
> ethernet routers: they use as short a cable as reasonable, but they
> should never use less than a couple of meters single length, right?

As you may have seen in my thread in this newsgroup I am facing
a problem with short cables and a specific PHY. So far I've never
heard of a "minimum cable length". Can you supply some details.

Thanks
- Rene

Rene wrote:
> "Rick Merrill" <RickMerrill@comTHROW.net> schrieb im Newsbeitrag
> news:JV8ic.10862$aQ6.875998@attbi_s51...
> 
>>Tauno Voipio wrote:
>>...> Admitted, the signal is RF, but the wavelength (even at the
>>
>>>third harmonic, 188 MHz) is well over a meter (little over a
>>>yard, for the foot-pound people), so a couple of millimeters is
>>>nothing.
>>
>>That reminds me of a common error when people wire up their own
>>ethernet routers: they use as short a cable as reasonable, but they
>>should never use less than a couple of meters single length, right?
> 
> 
> As you may have seen in my thread in this newsgroup I am facing
> a problem with short cables and a specific PHY. So far I've never
> heard of a "minimum cable length". Can you supply some details.

In brief, an ethernet cable is an antenna: If it is too short the 
reflected signals will create interference. The "minimum cable
length between workstations" (and between hubs) is "8 feet".
(That is for 10baseT) For 10Base2 the minimum is "20 inches".

- http://support.microsoft.com/default.aspx?scid=kb;en-us;Q97550

It is also vital to note that while many configuations will work, 
there are not "supposed" to be more than 4 hubs between ANY TWO
NIC.  This topology restriction derives from the time delays 
inherent in a hub. (Switches have different rules.) -  RM