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Using the 24AA025E48 I2C "mac address" chip with EtherBoards

Posted: Tue Jul 16, 2013 4:13 am
by bjh
Hi there,

In the comments of SuperHouse TV Ep #7 on the RFID reader, Jon mentions in one of his comments that he found a more slick way of coming up with unique MAC addresses for Ethernet connectivitiy than by using a 1-wire temp probe. The chip he mentioned is the "Microchip 24AA025E48" (Manufacturers page at: ... e=en548829, background info at: ... e=en542943) which is actually a purpose built chip - with each one containing a write-protected and unique MAC address on it. Brilliant!!

I'd love to use these with the FreeTronics EtherMega, and possibly even fit the chip in the nifty little prototyping space on this board. I'm not sure how to wire this chip up to talk to the controller board via I2C (nor the sketch code that would then be used to read the MAC address stored on the chip and set the parameters for the Ethernet adapter).

Has anyone had a play with these chips and worked out the details? Would anyone be able to provide a wiring guide and a snippet of code? The chips are really inexpensive, and combined with Freetronics improved Arduino boards which do away with the need for added shields, this could be a winning combo.

(In fact: Freetronics - would you consider in a future revision of your Etherboards including one of these IC's as standard? That would solve the most frequent challenge with connecting the Arduino's to Ethernet networks).

I apologise - I'm quite a noob to the whole Arduino world, so while I'm sure the answer to this question is dead simple, it still has me left scratching my head. I also couldn't find any blog articles, forum posts, etc that deal with the use of this chip with the Arduino as the optimal method of MAC address handling (even the Freetronics article still references the temp probe method of generating a unique ID, and because the first few octets of a legit MAC address are manufacturer reserved and issued by IANA, there's still a slim chance that the address created by using the temp probe's ID wouldn't be globally unique [nor kosher according to the networking standards]), so I'm sure there'd be a few grateful people out there if someone could help with the answer as to how to use this beautifully purpose-built MAC address chip, which is truly compliant with the Layer 2 MAC Addressing standards for uniqueness.

Thanks heaps in advance!


Re: Using the 24AA025E48 I2C "mac address" chip with EtherBo

Posted: Wed Jul 17, 2013 10:48 pm
by andrew
There's a few options for hard-coding the MAC address.
1) If you're not in a busting hurry we've got a new Ethernet-enabled board coming (hopefully) next month that has the 24AA025E48 installed :)

2) One of our resellers has a product that solves the problem but with an EEPROM - the details and design files are here:

3) They're an I2C device, so quite easy to connect. If you're not familiar with I2C see the data sheet and ... e-i2c-bus/.

Re: Using the 24AA025E48 I2C "mac address" chip with EtherBo

Posted: Wed Jul 17, 2013 11:58 pm
by bjh
Thanks for those pointers John!

That's great news that Freetronics will be including the chips on future boards. With the EtherMega supporting inbuilt PoE and its own unique MAC address chip - what an awesome combo!

I'll experiment with options 2 and 3 in the meantime.



Re: Using the 24AA025E48 I2C "mac address" chip with EtherBo

Posted: Fri Sep 06, 2013 1:12 am
by jonoxer
Slightly later than we hoped, but the good news is that v3 of the EtherMega just went into production last week with the MAC address chip included. That means we're about 6 to 8 weeks away from it being available for purchase.

Late last night I finished the update to the EtherTen to add the MAC chip, so the next production run for that will have it as well.

I've already updated the Ethernet Shield design to include it but we haven't put that into the production queue yet.

The EtherDue (which has just gone through its first prototyping round) already has it included from the start.

So very soon we'll have 4 different products with the MAC chip on it! It should be very handy.

Re: Using the 24AA025E48 I2C "mac address" chip with EtherBo

Posted: Fri Sep 06, 2013 3:12 am
by bjh
Nice work guys - look forward to working with the new boards!