Interfacing a Ethernet PHY in an unusual way

[stb_haag]

Hi,

I want to design a 10BaseT media converter using a dual channel PHY which is able to loop one channel to the other. At one channel I have the official 10BaseT interface ant at the second channel I try to adopt to TTL level. This TTL signal will be somehow transported and converted back to 10BaseT by another media converter.

My problem is the conversion from differential PHY interface to TTL and back.

Any ideas?

Thanks
Stefan

 

[FvM]

You could use a PHY with logic level signaling, e.g. intended for fibre-optic interface.

 

[stb_haag]

Actually, the fiber optics link was my first approach. The PHY provides RX and TX in PECL, so it is easy to convert to TTL. But unfortunately on the transmisson link between TTL interfaces can't handle the frequency of 62.5MHz (+hamonics a bandwidth on ~300MHz is needed). In FX-mode you get 100MBit/s and 125MBit/s due to 4B5B coding even if you use 10MBit/s only.

 

[FvM]

What you say doesn't apply to all fibre physical layers, I think. You should review e.g. 10BASE-FP.

 

[stb_haag]

Thanks for the hint. 10Base-FP is new for me. Maybe this could work.
Do you know if full duplex is possible? And - more important - can you recommend a PHY? I found CS8900 only. But it is single channel and as I explaned before I need two channels connected in a loop.

 

[FvM]

I can't recommend a PHY for it, I know the respective media standards only from the IEEE spec. I remember however, that 10 MBit only fibre links have been popular 15 or 20 years ago, so there should be a suitable hardware.

I also think that you should be able to convert the bipolar 10-BASE-T layer to an unipolar bit stream, because the zero level is used only during idle state, and the coding can be effectively reduced to "long" and "short" bits according to the specification. Another approach would be to design your own PHY using programmable logic and attach it to the media independant interface.