RJ45 connections

[richacm]

Hi,

I was hoping someone could check these connections for me. I have an RJ45 socket as specified in this diagram:
https://www.electro-tech-online.com/custompdfs/2008/09/0900766b807c5bb0.pdf

And I also have a ethernet controller chip from MicroChip as specified in this datasheet:
https://www.electro-tech-online.com/custompdfs/2008/09/39662c.pdf

If you look at page 9 (or 7 in PDF file) of the MicroChip datasheet you will see a circuit diagram for connecting the outputs from the ENC28J60 to an RJ45 socket. The question I have is that my RJ45 socket contains all the required external peices already for the ENC28J60....I just want to know what wires go with what on the socket.

So far I have:

ENC28J60                            RJ45
---------------------               ---------------
TPOUT+                              1  - TDP
                                    2  - TCT
TPOUT-                              3  - TDN
TPIN+                               4  - RDP
                                    5  - RCT
TPIN-                               6  - RCN
                                    7  - NC
                                    8  - ?

Can I just leave pins 2, 5, 7, and 8 unconnected on the RJ45? I'm thinking I need to connect up the Center-Tap connections so I can add a Ferrite Bead in there as well....I'm a bit confused as to how to do this though.

Thanks,

Craig

 

[chilinski]

Hmmm. Standard ethernet uses pins 1, 2, 3 and 6. The others aren't used under normal Cat5, etc., but you ALWAYS wire all eight.

See this:
**broken link removed**

Generally, it is okay to ignore the others, but it's "bad form" to do so.

Note that the color coding of the wire is important...not to the success of the circuit, but to anyone following behind you who would expect you to have followed the standard.

 

[rezer]

So far I have:

ENC28J60                            RJ45
---------------------               ---------------
TPOUT+                              1  - TDP
                                    2  - TCT
TPOUT-                              3  - TDN
TPIN+                               4  - RDP
                                    5  - RCT
TPIN-                               6  - RCN
                                    7  - NC
                                    8  - ?

Can I just leave pins 2, 5, 7, and 8 unconnected on the RJ45?

You will need to terminate pins 2,5,7 and 8 with a series 75 ohm resistor and 1nF cap to minimize reflections. You can tie pin 7 to pin 8 with the termination if you wish. With networking cable, you want to tie up your loose ends (termination).

 

[richacm]

OK, like the MicroChip circuit indicates on the RJ45 side of the transformers. So do I place a Ferrite bead on the TCT connection as well?

 

[rezer]

Are you referring to the ferrite bead on the secondary winding? What voltage is the microcontroller operating at? If it's 5V, than yes, the ferrite bead is required.

 

[richacm]

The microchip is running at 3V. I think I will put one on anyway.

Cheers,

Craig

 

[richacm]

Hmmm. Standard ethernet uses pins 1, 2, 3 and 6. The others aren't used under normal Cat5, etc., but you ALWAYS wire all eight.

See this:
**broken link removed**

Generally, it is okay to ignore the others, but it's "bad form" to do so.

Note that the color coding of the wire is important...not to the success of the circuit, but to anyone following behind you who would expect you to have followed the standard.

Yes it does use pins 1,2,3 and 6 for the RJ socket (see wiring diagram in last first post). The pins are attached differently than what is presented to the socket.

 

[richacm]

Are you referring to the ferrite bead on the secondary winding? What voltage is the microcontroller operating at? If it's 5V, than yes, the ferrite bead is required.

Hi, thanks for all the replies. I am still a bit confused where to put the Ferrite bead. Attached is my RJ45 socket connections as you've indicated (I hope) do I place the ferrite bead on the TCT wire from the socket?

Thanks,

Craig

 

[rezer]

Just to clarify, this RJ45 has the network transformer built in, correct? If so, the unused pins should already be terminated. They have to be because there is no way to gain access to them. Sorry, I missed a very important piece of your first post.
Yes, tie the ferrite bead in at pin 2 in series with a 0.1uF cap like the data sheet suggests.
You shouldn't have to tie anything to pins 7 and 8. These pins are open and not connected to the network.

 

[richacm]

Just to clarify, this RJ45 has the network transformer built in, correct? If so, the unused pins should already be terminated. They have to be because there is no way to gain access to them. Sorry, I missed a very important piece of your first post.
Yes, tie the ferrite bead in at pin 2 in series with a 0.1uF cap like the data sheet suggests.
You shouldn't have to tie anything to pins 7 and 8. These pins are open and not connected to the network.

Hmm, I'm getting more confused now sorry. So I just need to tie pin 2 and 5 to a 75Ω resistor in series with a 0.1uF capacitor and also place a ferrite bead on pin 2 to the 3V. That's all?

Yes the RJ45 has a transformer already built in like this datasheet shows:
https://www.electro-tech-online.com/custompdfs/2008/09/0900766b807c5bb0-1.pdf

Thanks,

Craig

 

[rezer]

Hmm, I'm getting more confused now sorry. So I just need to tie pin 2 and 5 to a 75Ω resistor in series with a 0.1uF capacitor and also place a ferrite bead on pin 2 to the 3V. That's all?

Yes the RJ45 has a transformer already built in like this datasheet shows:
https://www.electro-tech-online.com/custompdfs/2008/09/0900766b807c5bb0-2.pdf

Thanks,

Craig

No, I'm sorry. The confusion is probably mostly my fault because I did not read your post carefully enough. I thought you were using a standard RJ45 with an external transformer. Disregard everything I said except my last post.
Based on the data sheet for the RJ45, you need to connect your ferrite bead to pin 2 (TCT) to 3V and in series with a 0.1uF cap to ground. Pins 4,5,7,and 8 are tied together internally. Just tie a 75Ω resistor from pin 8 to shield ground, not signal ground. Pin 7 is not connected, you don't have to worry about that one. I hope this clears things.

 

[richacm]

Right, I think I've got it. Thanks a lot.

Attached is my understanding of what you are saying.

Cheers,

Craig

 

[rezer]

It looks good except you will want to keep your shield ground isolated from your signal ground at pins 10 and 11.