Hi team! Love the UNO R4 minima. Also love an adafruit 2.8” tft display shield. Both work great together. However, i need access to the R4 minima ports. Does anyone know of any commercial header that gives me access to all the R4 pins while supporting my display shield on top of it?!?! I find a lot of R3, but they are not fully compatible as this forum knows. I could buy large numbers so please let me know. Thanks for any guidance!!! Mark
In what way are they not compatible ?
Hi folks, a couple questions on why r3 and r4 are not compatible from a shield perspective.
You’ll notice more pins on each side of the board, in addition to the developer pins on top. But the key ones are on the side rails, such as scl and sda. Pic attached shows an “R3 compatible board” but is short several pins.
Thanks for enlightening me 
Note sure if the below helps
SDA and SCL are also available on A4 and A5 so that might only be a minor issue.
For the SWD you can consider a cable permanently connected; not really neat.
Amazon.com: Gikfun Screw Shield Expansion Board for Arduino UNO R3 EK7007 : Electronics clearly has de additional pin for BOOT as well as the additional SDA/SCL pins.
Thank you very much for that Amazon link! Placed the order and hoping that fills the gap. Really appreciate it!
Mark
@sterretje PS... it is a major issue because the Display shield uses SDA/SCL. (2.8" Adafruit Display). I think a lot more caution needs to be applied in these forums when assuming these R3 and R4 physical pins are compatible.
You are proceeding from a false premise. Because, for the header pins that go to a shield, they are.
Here's a picture of an Uno R3. Complete with SDA and SCL in the upper left and the IOREF and uncommitted pins in the lower left. Exactly the same an an R4.
Those extra pins were introduced with the R3.
Here's a picture of the Uno R2, which didn't have them.
Your R2 vintage screw shield wouldn't work any better with a shield that wanted to use the dedicated SCL, SDA or IOREF pins on an R3 or R4.
So, what exactly is your complaint?
Is it that you couldn't find a shield for the Uno that has terminal blocks for all the R3 footprint pins? If so, you didn't look very hard. The very first return I had when I searched for "uno screw header shield" was this:
@van_der_decken. No complaint at all! I ordered two from Amazon, and two from eBay, and both were identified as R3 compatible. When I got them, it's the one I showed in my picture. So I wrongly assumed these were R3 compatible as ordered, but according to your data they are not R3 compatible. Regardless I'm grateful for your posts, I just ordered those from Adafruit. Really really cool and you saved me a bunch of time. Reach out if I can help you in anyway. thanks! Mark
If the display shield is not compatible with the Uno R4 because it does not provide connections to the pins labelled SDA and SCL then it will also not ne compatible with a Uno R3 for the same reason
As has already been pointed out the marked pins are only there as a convenience (or to confuse people) because they are actually connected to A4 and A5
Display shield works amazing on the R4... but it is using SDA and SCL pins, not A4/A5. R4 is my target platform.
If you break out your ohm meter, you will find that SCL/SDA are connected to A4/A5 so there is no difference from a board perspective. I believe that is the point @UKHeliBob was making.
Yes, that was part of it, and @sterretje before me
In summary, there is no need to use the pins marked SDA and SCL and in addition if a shield does not provide a connection to those 2 pins on an R4 then it also won't provide a connection to them on an R3
This is true of Uno R3 and R4.
Some other boards (notably, Arduino Zero and compatibles, and the Uno WiFi Rev2) actually have separate chip pins for SCL/SDA.