ethernet jack griping

[Alex Eisenhut]

I'm trying to understand some things about this part:

http://www.digikey.ca/product-search/en?vendor=0&keywords=j0g-0001nl

1) There's no real standard for the meaning of the LEDs wrt to link speed, right? I haven't found anything.

2) Am I supposed to add C1 on my pcb on page 2, or is it already in the jack? And if it is, well, what pins are the "shield"?
On pg 3 they show pin # for everything, but nothing says "shield"! I guess the shield is the two pins for the case?
Is assuming good enough for design work?

TIA

[T3sl4co1l]

1. Dunno, inspect your computer's adapter to figure it out I guess.
2. That's the internal schematic.  Looks like they already have everything you need.
"3." Shield generally means the outer casing, so, yeah.  If no pin number (proper) is assigned, then it also doesn't connect to a pin.

If circuit ground and enclosure ground are the same (or you don't have a metallic enclosure), then you can connect shield to ground.  If they are different (often done for isolation purposes), connect shield to the enclosure.  Optionally, you can connect some capacitance from circuit ground to shield as an RF bypass, with suitable ratings for your isolation situation (i.e., AC-line-to-ground requires a Y1 type capacitor).

Tim

[miguelvp]

1) There's no real standard for the meaning of the LEDs wrt to link speed, right? I haven't found anything.

Orange is not full speed so 10/100Mbps link
Green is for full Gigabit speed 1000Mbps link

The yellow one is for activity.

if you google "ethernet orange green link light" you'll find plenty of information about it.

BTW there are some newer routers that use blue/green instead of green/orange.

[Alex Eisenhut]

LOL thanks, Ethernet is not my "thing" and I don't like assuming too much about things I've never used before. Even if it's dead simple stuff.

I don't get the shield thing, Ethernet UTP cabling is .. U. Unshielded. So what the hell is the shield for? It's just the sheet metal case that keeps the plastic from flying off the board during soldering. No? I guess there must be STP cabling?

As for the LEDs, those jacks are usually in the back or in such an inconvenient location that no one cares. Oh well.

[miguelvp]

IT does when they see your computer is not linked at full speed

Or you should at least when you connect it for the first time to make sure you are getting the full bandwidth.

Edit: BTW, some Ethernet link indicators use: Green 1Gpbs, Yellow 100Mbps, Off 10Mbps I didn't know that but thanks to your question I found that out.

http://docs.oracle.com/cd/E22693_01/doc.21/e23342/glvhg.html#autoId12

Also found out that the activity link can be green instead of yellow and they can be swapped like the link above.

[Alex Eisenhut]

IT does when they see your computer is not linked at full speed

Or you should at least when you connect it for the first time to make sure you are getting the full bandwidth.

Edit: BTW, some Ethernet link indicators use: Green 1Gpbs, Yellow 100Mbps, Off 10Mbps I didn't know that but thanks to your question I found that out.

http://docs.oracle.com/cd/E22693_01/doc.21/e23342/glvhg.html#autoId12

Also found out that the activity link can be green instead of yellow and they can be swapped like the link above.

Yeah that was the problem, it didn't look too standardized, and I can't recall the last time *I* looked at or even used a wired network...
Eh, I'll make the LEDs flash any way I feel like and I'll bet no one cares what they mean!

[miguelvp]

What PHY chip are you using? it should have pins to drive the LEDs like pins 7-10 in this datasheet (page 12) and explanation in page 67.

http://www.ti.com/lit/ds/symlink/dp83865.pdf

[Alex Eisenhut]

What PHY chip are you using? it should have pins to drive the LEDs like pins 7-10 in this datasheet (page 12) and explanation in page 67.

http://www.ti.com/lit/ds/symlink/dp83865.pdf

KSZ9031RNX
It has only two LED output pins.... but supports tri-color dual-LED mode. Yet there's no clear definition of what color means.

http://www.micrel.com/_PDF/Ethernet/datasheets/KSZ9031RNX.pdf
pg 28
The table just talks about "blinking". I'm no expert, but "blinking" is not a color.

I'm trying to figure out how this maps to the three LEDs in the jack.

[miguelvp]

Seems it has only a single led or dual led.

So in tricolor you can link LED2 to the green terminal and the LED1 to the Orange one and don't connect the yellow.


or in single LED mode LED1 to the yellow (activity) and LED2 to the Green (Link with no speed indication) and leave orange not connected.

Pin 41 LED_MODE strap-in selects the mode:
pull-up: Single-LED mode
pull-down: Tri-color dual LED mode

[Alex Eisenhut]

Seems it has only a single led or dual led.

So in tricolor you can link LED2 to the green terminal and the LED1 to the Orange one and don't connect the yellow.


or in single LED mode LED1 to the yellow (activity) and LED2 to the Green (Link with no speed indication) and leave orange not connected.

Pin 41 LED_MODE strap-in selects the mode:
pull-up: Single-LED mode
pull-down: Tri-color dual LED mode

Pretty much, there's no simple way to decode those trinary LED outputs into three binary outputs for the jack's LEDs.

[T3sl4co1l]

I don't get the shield thing, Ethernet UTP cabling is .. U. Unshielded. So what the hell is the shield for? It's just the sheet metal case that keeps the plastic from flying off the board during soldering. No? I guess there must be STP cabling?

There is, which I assume brings those shields up to the housing or something.  The main thing is a place for ESD to go.  It's a safety thing, so the shield has to connect to anything also environmental, so it can find a path to safety ground.

Tim

[David Hess]

BTW there are some newer routers that use blue/green instead of green/orange.

Of course there are.   

[David Hess]

I don't get the shield thing, Ethernet UTP cabling is .. U. Unshielded. So what the hell is the shield for? It's just the sheet metal case that keeps the plastic from flying off the board during soldering. No? I guess there must be STP cabling?

STP cable is used for Ethernet in adverse environments like radio towers and industrial areas.  There are special modular plugs which make contact with the metal shield and the drain wire in the cable.

[Kjelt]

I would do some proper research on how to connect the shield in respect to earth and the ground of your circuit. If not you could have issues like ground loops, shorts, etc.

[David Hess]

I would do some proper research on how to connect the shield in respect to earth and the ground of your circuit. If not you could have issues like ground loops, shorts, etc.

This is definitely a problem and I have no idea how different Ethernet equipment handles it.  I think the best case would be to connect the modular socket shields to chassis ground via a high voltage safety capacitor with a high value bleed resistor in parallel.

But I have seen so much equipment that connects the shield to ground directly that unless I can verify some type of galvanic isolation or know the equipment is using the same ground return (and maybe not even then), I either cut the shield connection on one side or do not use a shield.  This applies more to other interfaces which do not have the galvanic isolation that Ethernet has but using shielded twisted pair creates the same problem.

[ConKbot]

1) The cap is internal, otherwise the output center-taps would have to be brought out on their own pin (which they arent)
2) As far as a standard, not that I know of, most equipment has a label to explain what the link rate/activity lights mean
3) The shield pins are the small ones on the very perimeter of the drawing for the footprint. The bigger center ones are mechanical support pins. The could have labeled that better.

As far as grounding and ground loops, the shield goes to earth/chassis ground.  Thats why there are EMI fingers on the jack, plus its exposed metal that the user can touch.  As far as ground loops and what not, there is no problems with UTP, as there is no ground, the ethernet signal is transformer isolated, and the centertaps of the output has a 2kv cap to ground, which means it can handle a substantial amount of common mode voltage.   For STP, yes you are connecting the two grounds with the shielded cable, but it wont affect the ethernet link as its differential, and a much higher speed than most noise on the cable would be.   The shield on the jack is to contain any radiated EMI from the transformers, and also to keep common mode noise on your big long cable picks up from radiating inside your enclosure and causing problems. Or vice-versa. 

Dont needlessly use STP and it'll all be ok.

[SirNick]

Re: Ethernet blinkies... here's what I've seen as most common.

Of course, Link / Act normally share an LED -- green or yellow, rarely something else.  Blinks off with activity.

Speed / Duplex is totally up to the device and anything goes, but there are some common cases.  Normally, Duplex does not have an indicator at all.  For 100Mb, Speed will usually be Off=10Mb, On=100Mb when using a single (typically green or yellow) LED, or Yellow=10Mb, Green=100Mb for a bi-color LED.  For 1Gb, Speed will often either be Off=10Mb, Yellow=100Mb, Green=1000Mb; or Yellow=10/100Mb, Green=1000Mb, Off=10/100Mb, On=1000Mb, or some combination of Orange / Yellow / Green.

Some Gb devices have given up with link speed and just show you Link on one LED, and Act on the other.  And there are all kinds of custom variations.  E.g., some Cisco switches have a button you press to change the mode -- Link, Act, Speed, Duplex, PoE, etc.  Juniper EX switches have one LED that blinks once per second for 10Mb, 2/s for 100Mb, 3/s for 1000Mb, and then the other LED blinks with activity.

In reality, you're somewhat beholden to what your PHY gives you, which is probably why there are so many trends despite the lack of any standard.  With only a handful of vendors out there making the silicon, you're pretty much going to get variations of that vendor's chosen light show any time you use their IC -- with some token customization like blink speed and support for single or bi-color LEDs.

[Jeroen3]

Green is OK, that makes sense. There is a standard for colors of indicators. http://www.iprocessmart.com/techsmart/lightcodes.htm
Orange usually indicates a non-normal condition, for example 100 Mbit on Gigabit systems or 10 Mbit on Fast Ethernet systems.

Then the shielding, the capacitor shown on the diagrams is inside the module, between transformer center and the metal can. But, a 1nF 2kV capacitor is usually placed to connect your boards ground to socket shield. You don't want current running through shield! Which could happen if both sides are connected to ground and there is a potential difference.
Potential differences are the whole reason there are transformers in it anyway.

[David Hess]

As far as ground loops and what not, there is no problems with UTP, as there is no ground, the ethernet signal is transformer isolated, and the center taps of the output has a 2kv cap to ground, which means it can handle a substantial amount of common mode voltage.

This is what makes Ethernet so great for data acquisition and connections between instrumentation and what makes USB (and GPIB, and RS-232, etc.) so poor.  Ethernet includes galvanic isolation (at both ends!) for free and other interfaces have to have it added.  I wish something like the old optically isolated MIDI interface had become a standard for test equipment.

For STP, yes you are connecting the two grounds with the shielded cable, but it wont affect the ethernet link as its differential, and a much higher speed than most noise on the cable would be.   The shield on the jack is to contain any radiated EMI from the transformers, and also to keep common mode noise on your big long cable picks up from radiating inside your enclosure and causing problems. Or vice-versa.

This is still a problem for two reasons:

An open ground on one side can allow fault current to flow through the cable to the other ground with catastrophic results (better witnessed at a distance) but this issue applies to any ground to ground loop and maybe it is better to know that there is a significant ground fault rather than letting it remain hidden.

Ground currents in the cable can *still* cause errors in the differential Ethernet transmission if only because of common mode capacitive coupling through the transformers.  Ethernet is very resistant to this but data transmission errors still happen in extreme conditions where shielding of the cable while avoiding a ground loop will help.

With other types of analog and digital signalling, usually the best solution as far as noise is to connect the shield only at the receiver or transmitter.  I forget which but Analog Devices has a great application note discussing it.  Which one you pick largely becomes irrelevant when both sides receive and transmit.

Dont needlessly use STP and it'll all be ok.

I agree.

[ejeffrey]

If you really are worried about EMI and ground loops you can always just use fiber.  Switches with SFP ports and Gigabit fiber transceivers are actually pretty cheap these days, and you get complete electrical isolation.  That is recommended procedure for using ethernet between buildings even when they are within the 100 meter distance limit.