Northof49:
Where are the:Revision 3 of the board has the following new features:
1.0 pinout: added SDA and SCL pins that are near to the AREF pin
I can't see anything near the AREF pin labled as SDA or SCL.
Would these differ in any way from pins 20 and 21 that are labed as SDA and SCL? Still trying to figure out why I can make I2C work on my Duemilanove but not on my Mega 2560 R3.
Also, what is the purpose of the second, unlabled ICSP six pin header?
It's to allow ICSP programming of firmware to the USB serial converter chip.
The reason that arduino added two new I2C signals on the current version of Uno and Mega2560 board was to make life easier for shield manufactures that utilized I2C components on their shields, so that they would work on both kinds of boards, where prior it was more difficult and kludgy to make that so.