DP83867ERGZ-S-EVM: Basic SGMII configuration

Alex Laflamme

Part Number: DP83867ERGZ-S-EVM
Other Parts Discussed in Thread: DP83867E,

Hi everyone,

I am looking to build a 10/100/1000mb media converter using a DP83867E chip so I bought a DP83867ERGZ-S-EVM evaluation board to get started.

My setup goes as follows:

Open network --> Copper port on the TI eval board --> DP83867E chip --> 4 x 50ohm SMA cables (RX+, RX-, TX+, TX-) --> Broadcom SFP module evaluation board PN: HFBR-0571 (and I also tried directly through a Avago AFBR 5803Z)

I would like to use a four wire SGMII connection between the TI chip and the SFP module. At this time, I cannot get any kind of communication through it. I left everything as-is on the evaluation board, I'm reading up on setting the LED jumpers and the different modes at the moment.

I am a little green when it comes to this technology so any help is appreciated.

Thanks!

Alex.

over 8 years ago

0 Ross Pimentel over 8 years ago

TI__Mastermind 23675 points

Hi Alex,

You need to use an SGMII capable SFP (fiber transceiver). The one you listed supports only 100BASE-FX. This is not the same as SGMII.
This fiber transceiver supports SGMII:
belfuse.com/.../sfp-1gbt-03.pdf

Kind regards,
Ross

0 Alex Laflamme over 8 years ago in reply to Ross Pimentel

Prodigy 40 points

Thanks for the reply Ross!

Using an SGMII compatible SFP module makes sense... let me pick you brain about that if you don't mind.

From my limited knowledge/research on SGMII and SFP modules, I was under the impression that SGMII was "Media Independent" which I interpreted as "it doesn't matter what you connect to it, as long as it can communicate over 4 wires (RX TX pairs)". Now looking at the pinout of an SFP module, the only "data" signals I could find were 4 wires (RX TX pairs) which prompted me to get that Broadcom/Avago SFP eval board.

That board seemed like a good starting point to try out SFP modules since it took only 4 wires (Rx-TX pairs) as input and could connect easily to the TI eval board.

That being said, the SFP module that I am using is made by Trendnet and probably doesn't support SGMII (I will have to double check that) so that would be step one: sourcing a fibre SFP module that supports SGMII. That Belfuse module you posted says it does 10/100/1000. Do you know if they all do 10/100/1000 through SGMII or are there some single 10 or 100 or 1000 modules?

...and clearly I need to do a bit more research on SGMII and SFP modules, do you know of any good resources on the topic?

Thanks. this is very appreciated!

Alex.

[Edit]

I've been looking into it again this morning and figured out that SGMII was developed for 10/100/1000 Base-T (copper) communication. Would that mean that 1000 Base-SX will not work with an SGMII interface? If so, then how would I go about connecting a 1000 Base-SX SFP module to the DP83867E chip? (if that is even the right chip for the job at this point)

0 Ross Pimentel over 8 years ago in reply to Alex Laflamme

TI__Mastermind 23675 points

Hi Alex,

You are correct that the acronym SGMII is Serial Gigabit Media Independent Interface.
However, this is in reference to the ability for different MAC to attach to different media (i.e. copper, fiber, etc..).
It is not in reference to the actual digital media connection between the PHY and MAC. SGMII like the other xMII interfaces is defined by IEEE.
There are requirements for the interfaces to exchange data and status information correctly.
SGMII != 100BASE-FX

100BASE-FX is a PECL based interface (you can use other drivers with DC blocking caps), which exchanges information on the MDI and not the xMII. 100BASE-FX Ethernet PHY will connect to a Fiber transceiver (SFP) by sending NRZI info at 125MHz.

SGMII is a serdies based LVDS interface that exchanges information on the xMII interface. It can connect to a SGMII capable MAC, PHY or SFP.

Some SFP modules only support 100Mbps, 1Gps, 10Mbps, or a combination of them. Just depends on the type you get.

I think you should look into the difference between the MDI and the xMII. Additionally look at 100BASE-FX, SGMII and 1000BASE-X.
All of those topics should give you a clear idea of the differences.

In regards to your edit, SGMII was developed for a reduced pin count when using 1G capable PHYs. Originally, GMII was used and then RGMII, but both of these had high pin counts that required large ICs. SGMII allowed for a 4 pin solution and also helped reduce emissions seen with RGMII since RGMII is a single ended signal. 1000BASE-SX fiber transceivers conform on the fiber side to the SX standard. It is not in reference to the electrical connection. Most likely the 1000BASE-SX SFPs use SGMII. You should contact the vendor to clarify what electrical interface is used (not fiber).

The reason why you ran into issues originally though is because that transceiver was specifically designed for 100BASE-FX. It is a bit confusing I agree since 100BASE-FX typically uses NRZI for the electrical connection between the SFP and PHY.

Kind regards,
Ross

0 Nicholas Mariani9 over 8 years ago in reply to Alex Laflamme

TI__Intellectual 2100 points

Hey Alex,

Ross has given a very good answer for the info you are looking for. I thought I'd chime in and also mention that I found the text, "Ethernet the Definitive Guide: Designing and Managing Local Area Networks" by Spurgeon and Zimmerman to be helpful. It won't provide you amazingly in depth hardware principles in PHY design, but it will give you a good idea on how the different protocols work, are classified, and what systems are needed for Ethernet (What I think you might be looking for). It was very helpful to have a picture of how everything communicated before looking at designing my own hardware with it.

Nick

0 Alex Laflamme over 8 years ago in reply to Ross Pimentel

Prodigy 40 points

Ok sounds great. Thanks for your help Ross, I definitely have some good stuff to lookup in your answer. I'll do my homework, see if I can get that proof of concept working and if I get more specific questions along the way, I'll definitely be back!

Thanks again!
Alex.

0 Alex Laflamme over 8 years ago in reply to Nicholas Mariani9

Prodigy 40 points

Thanks for the reference Nicholas, I'll try to get a hold of that document.
Alex.

0 Bob C over 8 years ago in reply to Alex Laflamme

Intellectual 615 points

Hi Alex,

In addition to Cisco's SGMII spec, you'll want to have a copy of 802.3-2015. You can grab it for free from ieee.org:

standards.ieee.org/.../802.3-2015.zip

Refer to clauses 36 and 37 in section 3 for specification of 8B/10B coding, K codes, ordered sets, auto negotiation, etc.

Also, I posted an article yesterday on SGMII, and maybe you'll find it helpful: mindchasers.com/.../hw-sgmii-review

Please consider it a draft and shoot me an email if you find errors or would like to see additional info.

Good luck,

Bob

Interface

Interface forum

DP83867ERGZ-S-EVM: Basic SGMII configuration