Uno vs. Leonardo and the SeeedStudio Starter Shield Tick Tock

Other Hardware 3rd Party Boards
1

I've been using UNOs for several projects and have had great success (really an amazing platform). I recently picked up a couple of Leonardos (genuine) with the thought that I might need the extra I/O sometime. I was generally aware of the USB interface difference, but thought that they would be otherwise pretty iinterchangable.

I have a SeeedStudio Starter Shield (Tick Tock) which works just fine with the UNO. When I tried it with the Leo, everything except the clock functions work. From the simple schematic they provide, it looks like the clock chip is interfaced via SCL/SDA, pins A5 and A4.

Although the UNO R3 has separate SCL/SDA pins it seems like it still allows the use of A5/A4 for older shields. Does the Leo no longer do this? Is there some other difference with the Leo that I'm missing?

Thank you.

2

Looking at this pinout diagram the SDA/SCL pins are on D2 & D3 not A4/A5 like on the UNO.

3

Thank you. This explains it. Excellent information.

4

Still on the Leo question: If I'm using SCL/SDA, does that entirely prohibit me from using D2/D3 for other purposes, even if I declare them as INPUT? So essentially SCL/SDA are hardwired to D2/D3?

5

IraSch:
Still on the Leo question: If I'm using SCL/SDA, does that entirely prohibit me from using D2/D3 for other purposes, even if I declare them as INPUT? So essentially SCL/SDA are hardwired to D2/D3?

The safe answer is yes, you should not try using the pins for other purposes if your using them for I2C.