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[on:]

I'm not sure where to post this, but here goes ...

Below is a modified photo of the Uno Rev3 board, with annotations about the extra meanings of some pins (not printed on the board):



I personally find that when trying to hook up I2C or SPI, I can never remember which pin is SDA and which is SCL. Hopefully this photo will help others to quickly connect up their systems.

Earlier boards are similar except that they don't have the ICSP header for programming the USB interface chip, and the extra SDA/SCL sockets for use with I2C.

I find that the pins on the ICSP header (on the right) are useful for grabbing an extra +5/Gnd combination if I need to power other devices (or for hooking up a multimeter or logic analyzer).

[Reply #1 on:]

Thanks for sharing!

[Reply #2 on:]

You are welcome.

I've put the same photo on my website, with various annotations about what the abreviations (eg. I2C, SPI) mean, and some useful stuff about maximum ratings:

http://www.gammon.com.au/uno

[Reply #3 on:]

I can never remember which pin is SDA and which is SCL

SCL = Simply Connect Last (at least on an Arduino 328)

SDA = Shouldbe Dhe Ather (The other)   

[Reply #4 on:]

That mounting hole on the top left side was already hard to use and this time with the two additional pins it should be impossible to use now.

[Reply #5 on:]

Really?  I'm using that mounting hole just fine with an R2.  I suspect the R3 will be tight and might even require some shaving of the screw/bolt head, but it should still work just fine.

[Reply #6 on:]

Nice job Nick. Working on breadboards a lot, I have a cheat sheet (attached) which shows the DIP pin numbers, the Arduino pin numbers, and the AVR pin names.

That mounting hole on the top left side was already hard to use and this time with the two additional pins it should be impossible to use now.

True that. I wonder why they felt compelled to add redundant I2C pins. I've found the existing ones to be quite adequate...

[Reply #7 on:]

Thanks for the cheat sheet Jack. I do a lot of stand alone development (not using the Arduino board) and I always have to look up the pins. This will help a lot.

[Reply #8 on:]

why they felt compelled to add redundant I2C pins.

multiple cpu compatibility.   It won't always be the case that the I2C shares pins with the ADC, and it would be nice to have shields that continue to work.

It's the same issue as SPI on the existing Uno vs MEGA.  The original ethernet shield assumed that the SPI pins were D13..11, and it didn't work with the MEGA at all, without stringing jumpers all over...

[Reply #9 on:]

multiple cpu compatibility.

Makes sense. Thanks.

[Reply #10 on:]

Dumb question... Did they change the USB interface chip and, why does its firmware need to be upgraded?

[Reply #11 on:]

The older Uno had an Atmega8U2-MU USB interface. The Rev 3 Uno has an Atmega16U2-MU chip.

I presume the ability to upgrade the firmware is to allow for if it turns out to have some sort of bug, or maybe just for future expansion.

[Reply #12 on:]

 Here is a small part of the info from this link: http://www.ladyada.net/library/arduino/unofaq.html


  The USB controller chip has moved from an atmega8u2 (8K flash) to an atmega16u2 (16K flash). This does not mean that you have more flash or RAM for your sketches this upgrade is for the USB interface chip only. In theory this will mean that it will be easier to have low level USB interfaces such as MIDI/Joystick/Keyboard available. However these are only theoretical at this time, there is no example code or firmware which will actually do this.

[Reply #13 on:]

Nick,  you didn't mention the extra pins on the power header. I think one has no connection the other is +5v also, tho not labelled that on the card.

[Reply #14 on:]

True, not on the photo. I mention the IOREF pin on the page I linked to.

http://www.gammon.com.au/uno