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Thanks
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Date: 2006/03/13 17:01
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By: Queen
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Status: Visitor
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Thank you for this article, can I use another pic18 in this design?
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Pulse Transformers
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Date: 2006/03/13 17:02
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By: bily
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Status: Visitor
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hi Ian,
This is what they have in maplin
N78CC Pulse Tx 1:1 68 in Stock £3.99
N79CC Pulse Tx 1:1 + 1 22 in Stock £3.99
N80CC Pulse Tx 1:1High Iso 27 in Stock £3.99
Do you think we could just ignore these transformers, would
it work without them? or would it make the endpoints
unmatched?
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Re:Thanks
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Date: 2006/03/13 17:02
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By: Ian
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Status: Moderator
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Karma: 5
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| Posts: 85 |   |
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You can use an other 18f pic but you must make sure that it has an SPI port and enough memory.
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Re:Thanks
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Date: 2006/03/13 17:02
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By: queen
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Status: Visitor
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Hello,
please can you answer me if I can use the schematic design for enc28j60 with another type of pic18 as pic18f252, and can you send me the design to my mail.
thanks
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Re:Thanks
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Date: 2006/03/13 17:03
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By: Ian
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Status: Moderator
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Karma: 5
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| Posts: 85 | |
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If you look at the specs for the PIC18F2520 it has 32Kbytes of Program Memory and the PIC18F4620 which I used in my design has 64Kbytes. The stack takes about 80% of the program memory (without an external eeprom for the website) of a PIC18F4620 so it won't run on the pic18f252.
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Re:Pulse Transformers
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Date: 2006/03/13 17:03
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By: Ian
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Status: Moderator
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Karma: 5
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| Posts: 85 | |
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Bily,
Everything I have read so far about the magnetics empasise the importance of good, short, etc. connections between the magnetics component and the RJ45 connector. Im fairly sure ignoring the transformers is either a bad idea or just won't work.
Also without them I think you would very easily fry your ENC28J60 chip. The spec includes a capacitor on the RJ45 side of the magnetics upto 2kVolts. Without the magnetics voltages like that could do a fair amount of damage to your ethernet controller.
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Magnetics
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Date: 2006/03/13 17:04
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By: bily
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Status: Visitor
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The question is for what purpose we need the magnetics; the only way to know this is from the ethernet specifications, but I don't know were we find them.
Were are these high voltages supposedly coming from?
It may be that they are just protection against thunder storms in situations where the ethernet cables are partly outside and exposed to the elements. If this is the case I think it is safe to simply ignore them while prototyping (but not in the finished product).
You could probably try it yourself and see if it works, I am almost sure you would not damage your ENC.
Since the pulse transformer is 1:1 there are no impedance change issues. The only issue that could exists is dc voltage, transformers isolate dc voltages. If there is a dc voltage issue then possibly you could damage your ENC, but hey, wouldn't it be worth 2 pounds to have this knowledge?
Post edited by: mat, at: 2006/03/13 17:06
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Magnetics Link
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Date: 2006/03/13 17:05
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By: Ian
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Status: Moderator
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Karma: 5
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| Posts: 85 | |
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To quote an application note I just read for a different product.
The magnetics provide impedance matching, signal shaping and conditioning, high voltage isolation and common-mode noise reduction. 10/100 Base-T Ethernet utilizes Unshielded Twisted Pair (UTP) transmission cable. The UTP wiring is prone to noise pickup that leads to conducted and radiated noise emission. The magnetics help to filter out the noise, provide good signal integrity and good electrical isolation.
How to Connect a Wired Ethernet Port to the WiPort
Sounds like even it would work without the magnetics your not going to get the same performance or stablility, without the signal shaping your likely to get more erros and unlikely to get the same data rate.
I'm sure the knowledge is worth 2 pounds, if you send me 2 pounds I'll find out for you. 
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2 Pounds
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Date: 2006/03/13 17:08
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By: bily
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Status: Visitor
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I will first try it myself (I need to order all the parts first); then if it doesn't work without the magnetics I may send you a spare enc to do this little experiment.
At the moment I am going over the software changes that are required, and I actually have a question for you -
Firstly, did you use for the linker the 'i' version or the non 'i'?
Also, in configuration, did you switch off the WatchDog, as it is enabled, or did you leave it enabled?
Finally, when the turns ratio is 1:1 there is no impedance transformation
RL'= RL*(n1/n2)^2
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Re:Building an ENC28J60 Ethernet Dev Board
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Date: 2006/03/13 17:08
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By: xx
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Status: Visitor
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this project doesn't work, I have just done it.
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Re:Building an ENC28J60 Ethernet Dev Board
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Date: 2006/03/13 17:08
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By: Ian
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Status: Moderator
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Karma: 5
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Me and a few guys on the forum all have it running stably.
Could you be a bit more explicit?
If you disconnect the SPI bus between the PIC and the Ethernet controller and then plug in an Ethernet cable do any of the lights connected to the ENC light up?
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