If MACs and IP addresses are all different.
I read somewhere that there is no ethernet transformer on Ethernet Shield, could this cause problems.
@LMI:
I read somewhere
Huh? That's just not so! Not for the official Ethernet shield and I can't imagine it for any implementation. (Could I be wrong??? See Footnote.)
I mean, if you look at the schematic or at the board you don't see something that looks like a transformer, but
...drum roll. please...
The magnetics are in the RJ45 jack! Google SI-40138. There are lots of electrical and mechanical equivalents.
Regards,
Dave
Footnote:
"It's not what you don't know that kills you.
It's what you know that is just flat wrong."
--- (Sometimes attributed to) Mark Twain
If you take a closer look at most ethernet device you have, something clearly stands out, due to its size: the transformers. The arduino ethernet shield uses a non-isolated approach: a resistor divider. This is very unusual actually, see W5100 datasheet for an example. This might lead to electrical problems because it forces non-isolation, and might kill your controller or switch.
This thread.
http://www.arduino.cc/cgi-bin/yabb2/YaBB.pl?num=1275156413
Edit: This thread is from
TCP/IP without Ethernet Shield: any use for it ?
29.05.2010 at 20:06:53
Edit2: I am of course very happy if E shields hw is a very standard design, with transformers / magnetics. Are sure of this.
OK
I found some data for SI-40138. It seems to have transformers included. Only a sw person would call a transformer magnetics, but I have seen this term also.
So it seems there is wrong info in the link I gave. If some one has more or first hand info, I am happy to hear.
If you take a closer look at most ethernet device you have, something clearly stands out, due to its size: the transformers.
Well I am new here at Arduinoland, and I haven't read all of the old posts to check their correctness (I'm not a cop, you know), so I'll just say the following.
With all due respect to whoever wrote that: That's just one person's opinion. My observation is that many (most?) recent designs have magnetics integrated in with the RJ45 jacks. The extra board space and expense of placing transformers on mostly surface-mount boards made integrated magnetics more cost-effective several years ago. There may still be some designs with separate transformers, but most of them that I have seen lately do not have the little rectangular lumps that are the (non-integrated) magnetics.
The [A]rduino [E]thernet shield uses a non-isolated approach: a resistor divider.
Well, I don't know what Arduino Ethernet shield circuitry that guy was looking at, but the one that I am looking at shows a SI-40138 Ethernet jack. You know, the one with the
---wait for it---
Integrated Magnetics.
The resistors and capacitor in the vicinity of the SI-40138 terminate the USP (Unshielded Twisted Pair) Ethernet lines with their specified impedance to reduce crosstalk, in accordance with all standard Ethernet design practices, and they are really required. However, they do not constitute a "resistor divider" (whatever the heck that is) that somehow (magically?) gets stuff onto and off of the Ethernet without a transformer.
see W5100 datasheet for an example.
Well, the W5100 data sheet that I am looking at shows a block diagram with a
---wait for it---
Transformer.
Now, I don't see any actual application circuitry that shows a separate transformer or an integrated-magnetics transformer, but I really, really (really) believe that no sane designer would try to design an Ethernet board without transformer coupling.
Of course I could be wrong. Or my point of reference for "sanity" might have to be adjusted, but: I would really like to see a successful (robust, commercial-quality) Ethernet NIC design without magnetic coupling. Really. I mean, there is nothing that I can see in the data sheet about transformerless connection to Ethernet. Is there an App Note that does? I'd really like to see it. Really.
Only a sw person would call a transformer magnetics
If that's supposed to be some kind of wisecrack, that's OK I can take it. I'm tough. (See Footnote.)
Oh, wait, I forgot for a minute: I'm not a strictly "software person." I swing from both sides of the plate.
However, I think that's another statement of one person's opinion. Look at data sheets from manufacturers like Amphenol, Tyco, Molex, Falcon, Lantronics, etc. and you will find phrases like
---wait for it---
Integrated Magnetics.
Why don't you Google something like Ethernet integrated magnetics and see how many of those data sheets you think were written by some "software person."
I could go on (and on and on...), but the Keepers are coming for me now, and I must flee.
Regards,
Dave
Footnote:
"I disapprove of what you say,
but I will defend to the death your right to say it"
---Often attributed to Voltaire
But actually coined by Evelyn Beatrice Hall
in the publication The Friends of Voltaire
"I may not agree with everything you say,
but I will defend to the death my right
to mock you."
---davekw7x
(It's almost certainly not original with me,
but I can'tremember where I heard it first.
I mean, it could be from those dang voices
in my head, but...)
If MACs and IP addresses are all different.
Oh, you know, about 4billion. More with NAT hacks, less if you want to interconnect with an existing internet that is using some of the IP address space. You'll need many megabucks worth of routers and stuff as well as the arduinos, of course. Step right this way...
could [not having an ethernet transformer] cause problems.
Not since it's not true! Even if it were true, the lack would be overcome at the first hub or switch that the Arduino connected to (IIRC, the theory that you can get away without magnetics is based on the idea that your direct connection is to a box that DOES have magnetics.) It might interfere with a direct connection (via "flipped" rj45 cable.)
(max number of nodes on a XXbaseT ethernet without special external hardware: 2. Normally you'll have a hub, switch, or router that you connect to.)