advantages of ethernet MAC ip core

It's all about trade-offs, isn't it? Do you want to one large lump sum, or a little at a time over a long period? Do you have board space? Spare I/O? Voltage rails available? Do you need the PHY layer, or are you paying for something you won't put to good use?

Have fun,

Marc

If you want to do ethernet you need both a MAC and PHY.

The MAC is a CPU to PHY interface. Some CPUs have it built in and a few PHYs have it built in. Unlike the PHY, a MAC is purely digital and can be designed into an FPGA.

If you are making thousands of boards, or have space constraints, a MAC core might make sense. If you are just making a few hundred, stick to commercial parts.

-- Mike Treseler

Actually, if you accept a few restrictions, you can do it all in the FPGA with very little outside electronics. I've got good success with 10BASE-T

Jean

Do you need a PLL to do it? I thought it would, but maybe not.

For 100baseTX you need three voltage levels. Maybe two outputs and appropriate resistors would work. Detecting three voltages on input will be hard, though.

You still need the transformer, which usually doesn't come in an FPGA.

-- glen

No, I didn't use any PLL so far. For receiving, I oversampled the signal (possible since 10BASE-T is so slow) and for transmitting I used a 20MHz clock.

100BASE-T would surely have been more difficult, first the signal looks like 125MHz, and now you mention this 3 voltage signals...

I didn't use any transformer, used capacitive coupling for the receiver, and direct coupling for the transmitter... works in the lab! A transformer might be necessary in real life for security or reliability reasons? Jean

FPGA

On a sunny day (Sun, 14 Dec 2003 07:48:34 GMT) it happened "Jean Nicolle" wrote in :

I have also build that little differential amp from fpga-fun site. Not all working yet (no time). I have not looked up the 100BASE-T spec yet, but 3 voltage levels can be done using 2 banks with 2 different references? For a 100MHz transformer, remember those 300Ohm to 75 coax VHF transformers? Every old TV had one, just a ferrite core with 3 or 4 turns... But my ethernet card was only 5.80 Euro, (6 $), there is a small transformer on it. So for 6 $ you have a transformer. Dunno how they can make these cards for that price. J

You can remove the cost variable from the equation. Check

They offer open source code for numerous cores, including a MAC PHY with associated test bench, and documentation. According to the "Status Log" for this core, it has been already tested in HW, and has been used in several commercial implementations.

The reasons for implementing functions in FPGA vs discrete IC implementation, are all very generic :

[1] Probable reduction in IC count, probable associated cost reduction, and probable increase in reliability. [2] Eliminate future redesigns of PWB when an external part experiences end-of-life. [3] Ability to "contain" majority of digital logic within single device simplifies clock domain management for synchronous design - ie. moves from a PWB/chip-to-chip problem to a single chip problem .. where it is much easier to manage.

--
Regards,
John Retta

I found the MAC, but the only PHY listed is for USB.

-- Mike Treseler

That is correct. No Phy. My mistake in original email.

--
Regards,
John Retta

(snip)

There should be a DIP package near the RJ45 jack, which is three little ferrite transformers in one package. About like the TV ones, only even smaller.

-- glen

Didn't you mean this OpenCores project?

It is an Ethernet MAC using the MII interface to connect to every PHY you want! I used the core in Altera FPGAs and have had no problems with it.

Regards, Marc

e-mail: Marc dot Colling at MaCo-Engineering dot de

want!

Which PHY did you use? I have LAN91C111 but don't know whether it can be used only as the PHY!?

Regards

Hi John,

the LAN91C111 has an external MII interface and it seems to be possible to disable the internal PHY (and use this MII for an external PHY). If it works also the other way round I have no idea, never tried it.

I used the folowing PHYs together with the OpenCores MAC: Broadcom BCM5201, AMD AM79C874 NetPHY, National Semi DP83865.

What kind of hardware do you use?

Regards, Marc

e-mail: Marc dot Colling at MaCo-Engineering dot de

Hi I am working with Altera Nios Kit with LAN91C111! Regards

you