Questions tagged [ethernet]

Questions about the electrical implementation of Ethernet; ask another Stack Exchange for software or protocol questions. Specify the speed as 10/100BASE-T is somewhat different from 1000BASE-T, apart form the speed. Those are copper standards; Ethernet over fiber optical cable is also defined.

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Should chassis ground be attached to digital ground?

I'm working on a PCB that has shielded RJ45 (ethernet), RS232, and USB connectors, and is powered by a 12V AC/DC brick power adapter (I do the 5V and 3.3V step down on board). The entire design is ...
99
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4answers
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Why Are Ethernet/RJ45 Sockets Magnetically Coupled?

As the title says really, why do ethernet sockets need to be mag-coupled? I have a basic understanding of electronics, but mostly, I can't figure out the right search terms to google this properly.
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20answers
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What is a good microcontroller for Ethernet applications?

What is a good microcontroller for doing Ethernet applications? Or do I just need a good Ethernet library to connect with an Ethernet MAC/PHY?
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10answers
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Why is an Ethernet cable not grounded?

There is no dedicated GND in the classical Ethernet 8P8C ("RJ45") pinout.[1] Why does the Ethernet spec not include a ground, unlike many other cable types used for interconnecting devices that may ...
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4answers
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Why is Ethernet So Power Hungry?

I was just perusing the Microchip ENC28J60 Ethernet Controller datasheet and saw that the operating current can be as high as 180mA while transmitting and 120 mA typical while active but not ...
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3answers
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How does a 40 Gbit/s Ethernet interface process packets in silicon?

A 40 Gbit/s Ethernet interface should have a 40 GHz signal on it. How does common silicon IC technology handle such an exotic beast? My best guess is that internally various parallel busses are used, ...
23
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3answers
34k views

what is the difference between PHY and MAC chip

I want to know what is the difference between PHY and MAC chip
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4answers
24k views

Very Long Distance Ethernet connection for Internet and other data (2000 feet)

I am building a house. It's located about 2000 feet away from the nearest Internet cable. I had to run our electrical service underground the whole way, and have already installed a conduit for ...
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3answers
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How is 10G Ethernet physically possible? [closed]

10 gigabit Ethernet means that 10 billion bits are transmitted every second, but I don't understand how this is physically possible (let alone 100G Ethernet). The fastest CPUs today only run at ~8GHz, ...
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3answers
936 views

Microcontroller with both ethernet and radio onboard?

Does anyone know of any (reasonably low-cost) SoC which combines all of: Microcontroller (any architecture, at least 4KB RAM/8KB flash) Radio transceiver (433MHz - 915MHz or 2.4GHz) Ethernet MAC + ...
20
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8answers
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Cheapest way to add wifi to a project [duplicate]

I need low power wifi for a not-very-data-intensive application. What modules or chipsets should I look at? Other than low cost and low power, I have no restrictions. The cheaper the better. This ...
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3answers
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Do magnetics connectors exist?

Conventional connectors, where the plug and socket have metal parts which touch, suffer from the following problems: Limited mating cycles or expensive plating. Impedance mismatch (relevant for high ...
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8answers
33k views

Communication between multiple microcontrollers

I'd like to start implementing a system consisting of N microcontrollers (N >= 2 MCUs), but I would like to know the possibilities to let them communicate one with the other. Ideally, (N-1) ...
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5answers
59k views

Difference between Hz and bps

Does Hz and bps mean same? Can a signal be transferred at rate of say Mbps on a channel bandwidth of few Khz?
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1answer
2k views

Reasoning behind Ethernet pair order

An Ethernet connector seems to use a surprising choice of signal placement in its RJ45 connector. Does anyone know the reasoning behind: The decision to make pair 2 straddle pair 1? Why Ethernet uses ...
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7answers
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What if there are an odd number of twists in a twisted pair cable?

I am not an electrician, or a student of the field. I am a Network Engineer with a curiosity bug and that has recently taken me to exploring cabling and Twisted Pair specifically. I say this to plead ...
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4answers
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Are solder bridges on chips always bad?

I just bought my Arduino Ethernet shield – a knock-off one for $10 instead of $60. I connected it up, but it doesn’t work – LEDs light up but do not blink, and no ethernet link is established (...
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2answers
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Why does this isolation transformer have another transformer in it?

The isolation transformer I'm looking at: http://www.mouser.com/ds/2/336/HX1188NL-515471.pdf My question is why is it there? Is it not enough to have just the transformer on the left?
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2answers
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Ethernet Without Magnetics?

How / can you connect Ethernet devices together without magnetics? How do you wire it up? What sorts of practical limitations are there on doing this? To clarify, I'm not trying to connect two ...
13
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3answers
6k views

How to Connect USB/Ethernet Shields to Chassis or Digital Grounds

I have a PCB with a few USB and RJ-45 Ethernet connectors on one side. I'm quite confused as to how exactly I'm supposed to be hooking up the SHIELD pins on them though. This is for a host device ...
13
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4answers
7k views

Building a passive ethernet hub with anti-parallel diodes

I've found several guides online on how to build a passive ethernet hub, the design is always the same: I'm wondering what each of the 2 anti-parallel diodes do? For both positive and negative ...
13
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3answers
14k views

Ethernet Layout Guidelines

I'm working on a DC jack powered Ethernet design and I've downloaded many Ethernet Layout guidelines from many semi vendors with varying recommendations. I've read app notes recommending almost every ...
13
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1answer
3k views

Why is Ethernet not intrinsically safe?

I understand from a training session that ProfiBUS is considered intrinsically safe, while ProfiNET is not. Some googling indicates that ProfiNET can never be intrinsically safe, because Ethernet can ...
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3answers
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Can the fake USB flash drive attack happen over Ethernet?

You may have seen the article This USB Drive Can Nuke A Computer where it shows how a flash drive shaped device can completely fry out all the components of a computer. This is very shocking (pun ...
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2answers
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Connecting ethernet to AVR

I am getting pretty familiar with microcontrollers and now want to connect it to the internet. What are the minimum requirements for a microcontroller to be able to do this, specifically, an AVR one ...
11
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1answer
2k views

How could I power an IC over the Ethernet?

I was looking foward to powering a small Integrated Circuit using only the power provided by the ethernet outlet of my room. Is that even possible? I've googled and I've found that the voltage that ...
11
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1answer
5k views

Bob Smith Termination with POE

I'm looking into doing a Bob Smith termination for a Power over Ethernet (POE) PSE. The TI app note shows the following termination: But all of TI's reference designs (and later figures in the same ...
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6answers
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What is the difference between Ethernet and Serial communication?

All the mouse movements, USB connections and other PC peripherals such as printers etc. are what is called serial communication. One bit per time. So far so good. But when it comes to TCP protocol, ...
10
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3answers
4k views

Do all PHY Ethernet chips have a hard-coded MAC address?

For example, this TI PHY chip DP83630 has two MAC addresses that can be used as destination and source MAC addresses for PHY control frames. (page 72 and 94) Does this means all PHY chips will have ...
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4answers
25k views

Connecting two Ethernet PHY without magnetics?

In a (tentative) new design I want to connect two 100 Mbit/s Ethernet PHY similar to LAN8270a, separated by few inches on the same PCB, with same ground plane (but different power supplies). I have ...
10
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1answer
6k views

What are the 49.9 ohm resistors for in this circuit?

I was wondering what do the 49.9 ohm resistors do in this circuit? Are they absolutely required since I don't have any that size.
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5answers
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Arduino or PIC microcontroller?

I was thinking of creating a surveillance mobile robot. And I am having a problem of choosing a PIC or a Arduino microcontroller. The surveillance mobile robot is controlled via wireless fidelity (Wi-...
10
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3answers
816 views

How much mains leakage does an Ethernet connection to a PC induce, and what is the operating leakage path?

It seems that some users on another Stack have reported GFCI nuisance trips caused by mains leakage through twisted-pair Ethernet cables connected between computers on different branch circuits, or ...
9
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3answers
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How important is the shield on an RJ45 connector?

If I am going to use a PCB mount RJ45 connector for 100mbps Ethernet, does it need to be a shielded connector, or can I get away with using an unshielded one? Is there some standard which deals with ...
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3answers
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USB vs Ethernet cable length

I was talking to a colleague about the limitations of USB cable length and as far as I could remember it was limited by the tight window the host requires the device to respond in (mentioned here). ...
9
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2answers
4k views

Poor eye diagram, where to start looking?

I'm trying to debug a 100Mbit ethernet board and I'm running up against a problem I'm having trouble trying to resolve. This is the eye diagram for the transmit pair. The receive pair is very similar....
9
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2answers
7k views

Ethernet: how important is the magnetics topology?

I have some Ethernet issues with a set of boards (6/10 are bad). They're possibly just assembly house mistakes... but I'm very concerned about my magnetics jack. I could have sworn I saw a example ...
9
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2answers
7k views

Effects of impedance matching between 50 and 75 Ohm coaxial cables for 10 Mbit/s, Manchester-coded signals (20 MHz)

TL,DR: This is quite a bunch of text because I have included plenty of background info. However, there will finally be a good, and precise question: Should I use an impedance matching network when ...
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2answers
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How can this layout be improved? (Gigabit Ethernet with discrete magnetics and POE)

Answer: No there is nothing majorly wrong with the layout, it turns out that the ethernet transformer was out of spec by 0.2dB on Insertion loss, when paired with the PHY IC we are using. Question ...
9
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1answer
1k views

What is the function of this choke-like transformer on the PCB side of this RJ45 jack+magnetics connector?

I came across this ethernet jack+magnetics connector the other day and was wondering what the transformer on the PCB side was for. I thought it looked like a choke, but there is a centre tap running ...
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1answer
2k views

Ethernet: distance from PHY to magnetics

I am confused as to the preferred placement of Ethernet PHY and magnetics. I thought that in general, the closer the better. But then SMSC/Microchip app note (http://ww1.microchip.com/downloads/en/...
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3answers
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How does “bidirectional” transmission on gigabit ethernet work?

I was reading about the various twisted pair protocols, being distracted by the marvels of Wikipedia when I went to look up the way to wire a connector. And I'm wondering how it can transmit in both ...
8
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4answers
1k views

What is needed to go from single Ethernet to many?

I have an embedded Linux system with a single Ethernet port, but I need to go to many ports. It is obvious I need to add magnetics and ports. The trickier parts follow. My processor has an on-board ...
8
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3answers
15k views

Connection of center tap for Ethernet transformer

I'm trying to connect an RJ-45 jack with integrated magnetics (Belfuse L829-1X1T-91 datasheet) to an Ethernet PHY chip (Micrel KSZ8041TL datasheet). The TX+/-, RX+/-, and the LED pins are all easy ...
8
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2answers
663 views

ETH PHY Protection during “no supply” condition

My quesiton is simple: In a typical ethernet setup, the RJ-45 jack connects via some transformers (or call it magnetics if you like to) to the Ethernet PHY. (which might be internal to the ...
8
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3answers
13k views

How do network devices detect whether an ethernet cable is connected?

I have a bit of kit with an FPGA on it which includes an ethernet adapter. I'm trying to diagnose why it's not working and while I do that I've noticed that with an ethernet cable connected to my ...
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3answers
884 views

Connecting TVS before or behind Ethernet transformer?

I looked at several designs and recomendations. Why do TVS diodes sometimes connect before and behind transformer? What are the pros and cons of connecting before or behind?
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2answers
9k views

Length Matching Differential Pairs

I am routing a PCB with an Ethernet connection and I am having a bit of trouble deciding on how best to route the TX and RX differential pairs. I have done the impedance calculations to figure out the ...
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3answers
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Schematic Critique: Phy interface with RJ45/Magnetics

I'm working on my first major schematic design and would really appreciate some feedback on the analog side of the 1000BASE-T Ethernet interface. I'm mostly concerned about the analog line termination ...
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4answers
9k views

Wiznet W5100 vs. Microchip ENCx24J600

What are pros and cons using Wiznet W5100 or Microchip EncX24J600? It's a bit complicated to explain. My question is about the performance of Microchip TCP stack vs Wiznet TCP/IP core on the chip. ...