[SI-LIST] Re: problems about 1-to-2 FE connection
- From: "npischl" <npischl@xxxxxxxxx>
- To: si-list@xxxxxxxxxxxxx
- Date: Wed, 24 Dec 2003 01:23:21 -0000
If I understand correctly, by "1-to-2 transformer" you don't mean the
turn ratio, but that the diff-pair routing on the switch-side is
paralleled from the transformer to the two switches.
In that case, and IF (and only IF)
1) you always have two switch boards plugged in
2) the length between the transformer (on the processor board)and the
PHYs(actually termination) on both switch boards is equal (meaning
the switch boards are in symmetrical slots relative to the processor)
then consider using 1:sqroot(2) transformer ratio to bring back the
impedance from 50 ohm (100||100) to the required 100 Ohm.
Neven
--- In si-list@xxxxxxxxxxxxxxx, "peter zhu" <peter.zhu@xxxx> wrote:
> Hi,experts:
>
> Very tough problem for me in Ethernet redundancy design.
>
> In our backplane, we use an illegal Ethernet switch board
redundancy scheme. our processor board has one FE(Fast Ethernet), and
two switch boards are resided in backplane for redundancy. the
processor board FE connect to the two switch board at the same time,
but one switch board is in standby state(The PHY on this board is
tristated), so the processor board FE will communication with the
active switch board. But you know, FE must have a transformer for
isolation, so the processor board FE has 1-to-2 transformer
connection because of the two switch board on this FE. This will
cause to Ethernt singal distortion and this is not compliant with
standard, and some processor boards can not transmit data with very
high speed.
>
> If we use AC104QF from Broadcom, maybe 2 boards FE will fail among
12 boards, other 10 boards FE are very normal.
>
> But if we use AM79C875KI from AMD, maybe 5 boards FE will fail
among 12 boards.
>
> Our redundancy scheme is not changeable, so how to let the FE work
nomal in this situation?
> Does anyone encounter similar problems?
>
> Urgent, I very appreciate your help and information.
>
>
> Thanks!
>
> Peter
>
> UTStarocm
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