Discovered a 16u2 secret header on Uno and Mega boards!

Other Hardware Device Hacking
1

Hey all, newbie here from China and please kindly forgive my poor English :slight_smile:

I discovered an unpopulated 4-pin header near the 16u2 ICSP header on the R3 version of arduino Uno and Mega board. I've been using all Cheap Chinese clones but it seems that official versions have them too! (see the official picture) Strangely, this header, briefly silk screened "JP5", did not appear anywhere according to the EAGLE board design files.

I tried to follow the trace on PCB and it looks like it is connected to the Pin18-21, the four unused GPIO pins of 16u2. These pins on the official schematics are left "Unconnected", but obviously they are there. :smiley:

So may I have anyone come at look at this and produce a firmware hack so that they can be used? 16u2 GPIOs might be very useful when it comes to firmware-level features (e.g. buttons that enable/disable sketch uploads, change 16u2's USB characteristics etc.), or simply expansion (for Uno). I'd be glad to see they can be made some use with.

Attached are pictures of relevant information. Thank you:)

QQ20140515-2.jpg
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QQ20140515-3.jpg
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QQ20140515-4.jpg
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2014-05-15 195402.jpg
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2

This header (or better the holes for it) is clearly visible in the R3 schematics of the UNO (JP2) and the Mega2560 (JP5), so I cannot see what's secret about that.

unor3_jp2.png

3

Ah-oh so maybe I'm holding on to a different version of schematics... But, is there a way to do something on it? :slight_smile:

4

Sure there is. Modify the firmware of the ATmega16U2 to use this pins, it's that easy.

You already described some interesting uses for these pins, another one could be to reset a shield without resetting the Arduino.