Also, match signal path lengths to minimize relative skew.
Jeff Condit
- Original Message -
From: Jason Morgan [EMAIL PROTECTED]
To: Protel EDA Forum [EMAIL PROTECTED]
Sent: Wednesday, September 22, 2004 2:48 AM
Subject: Re: [PEDA] Ethernet Connection
It depends on many things, but I don't think you need to use an extra
internal RJ45, unless there is a manufacturing reason for it.
I use internal Ethernet in all our products.
You need to take into account:
Ethernet speed - 10baseT and you'll probably be OK, 100Base or faster and
you need to be very careful.
Location of components, keep the internal Ethernet lengths as short as
possible.
Trace impedance - keep the trace impedance as close to 100 Ohms as
possible.
Discontinuity - there will be an impedance discontinuity at the connector.
If its 10Base, and the components are close to the connector, and the
traces are short, there should be little trouble.
If its 100Base, the components are well separated, and the lines are long,
then you'll probably be in trouble.
Lets call the external connector board 'LEFT', and the internal
electronics board 'RIGHT'.
Obviously, I don't know your design, but you could mount the PHY and the
magnetics on the LEFT, then use the much slower and synchronous MII to
interface to the MAC on the RIGHT.
In any case, always put the magnetics as close to the RJ connector as
possible, use magjacks if possible.
You could remove the problem by choosing an impedance matched connector,
but these are much more expensive.
Download Polar si8000 from their website, they do a pay-as-you-go
version that will help you make sure your trace design is correct.
Don't trust Protel's 'Impedance matching' in all but a few cases, its way
off the mark, just compare polars 'real world models' with protels textbook
generic formula and you'll see what I mean.
Depending on your board construction, make use of broadside stripline or
edge coupled differential traces, this will help you get the impedance you
want.
If you have use of a network analyser and don't think twice about sending
PCBs to fab then your job is easy, just make prototypes until its right.
If you have totally internal Ethernet connections, have a search for
application notes on using 'transformerless' or 'capacitive' coupling
between PHYs, this will save loads.
Hope this all helps,
Jason.
-Original Message-
From: Back, Norb [mailto:[EMAIL PROTECTED]
Sent: 21 September 2004 19:26
To: Protel EDA Forum
Subject: [PEDA] Ethernet Connection
Importance: High
Hi all
First time for a Ethernet connection
The layout calls for all out side connections (RJ-45 jack) to be on one
board and mate with a mother board
threw a 125 pin mating connector, down the mother bd to were a TINI bd
will be mounted
Or would putting another RJ-45 jack on the mother bd right next to the
125 pin connector
And use a Ethernet patch cord to the TINI bd be better?
The connection bd and mother bd need to be able to separate
Any help or tricks
Still using 99SE
Thanks
Norbert J Back C.I.D.
Engineering Technician
Gilson Inc.
3000 W. Beltline Hwy.
Middleton, WI. 53562
PH 1- 800-445-7661 ex-4438
Fax 608-821-4498
[EMAIL PROTECTED]
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