*Update: Both Uno R3 and Ethernet Shield SD R3 are now available from the online shop. A bundle of both or other such promotion should appear shortly. 

I have been holding this two weird (yet no less than the latest) version of Arduino and shield for about a week now. Playing around with it as well as exploring their irregularity.

As distributor, R3 version of Arduino was made known to H&T back in November 2011. But only now I get the chance to play with them. Fear not, might be a bit behind schedule, but perhaps shine more in completeness. Right here there are both Uno R3 and R3 shield. As well as previous version of Uno to compare.

Here are the two new products ... <drum rolls!> ... in boxes

Well, in a box the new Uno (let's just called it Uno R3 henceforth) does not really look any different.

The surprise is that, the new Ethernet Shield (let's just called it Eth R3 henceforth and be merry ;D) come in a box much like Uno but larger. Which also means you get free stickers, as well as a big thank you note. Buy it together with Uno and you get more of these!

Unboxed

The front shows this model is without POE

The back shows that this is R3. Click to enlarge and Look for Ethernet R3 at bottom left corner

  

The Uno R3 packaging is the same. How to tell between R3 and older version?

Well to be honest, there was never Uno R1. The first Uno is simply just Uno. But that bring up the question about R2. Also, the most curious will even ask why use R as in revision and not V as in version. 

Using revision instead of version implies that small changes is made to the board, hence the R. To continue with this reasoning, R2 is very small revision that does not warrant much celebration. So it was silently release to the market.

But R3 is special, ain't it? Otherwise we will not be reading this article.

I am going to write more about this in future article. However let's shoot straight directly to the concern of physical compatibilities. After all, there are  additional pins for the new revision. Do remember that R3 applies to Arduino board as well as shields that want to be fully compatible with the R3 revision.

In case 1, it is a given that older revision of shield will not have the additional pins as in R3 revision. The shield will work as intended. Additional note about stacking shield. If there is mix between R3 and non R3 shield, would be good idea to put non R3 shields on top. Since non R3 shields do not pass additional pins interface to top shield.

In case 2, both R3 board and R3 shield as intended. 

In case 3, is what happen when previous revision board is used with an R3 shields. Physically, the extra pins are not really compatible with older revision board.

Not really! That does not looks good, does it? Well, we are in DIY field. As work around, it would be easy to bend the pins using pliers. Or worst case scenario, to cut it as nice as possible.

IMHO, it will slowdown adoption of new R3 shield by third party manufacturer. In the beginning, there will be a lot more of non R3 board compared to the new R3 board. But from the looks of it, Arduino people from Italy are really commited with supplying R3 boards. For instance, it is harder for distributor to get previous revision of Uno at the moment.

So as R3 board become more prevalence in the market. More buyer will prefer shield that follow R3 revision. Hence, third party manufacturer will be happier to make and supply some. Perhaps by then, there will be a better work around at having R3 shield that work with non R3 board?

Amazing how we are nearly near the end of the article without any clear mention about what is actually new with Uno R3. Will let a picture do the talking shortly. However, to summarize things up (in textual form that is). Arduino R3 is a minor release. Your existing code and shield should work with it the same as previous revision of Uno. If it does not works, perhaps it is Arduino IDE 1.0 that is the problem? Well that is another story and should be in a different article soon. (Hint: Arduino Uno R3 require Arduino IDE 1.0 to install the hardware driver. If there is code issue or library having compile error, switch back to previous version of IDE and your code will work again!)

There happened to be additional 4 pinout on the board. However 2 of it (SDA and SCL) are duplicate of A4 and A5 pin which also function similarly to facilitate I2C or TWI communication. As  for the other two pinout among the power headers. The first one is not connected at all and simply reserved for future design. The second pinout, labelled as IOREF. Is a little bit vague functionality wise. My understanding is that it will allow future shield to check I/O voltage level of the underlying Arduino board, be it 3.3v or 5v. Definitely this will require further investigation.

With that said, there are other small changes such as using ATMEGA16U instead of ATMEGA8U. But I am getting ahead of my self. Lets bellow graphic do the talking and have fun!