**Question:** What registers do I use to access the IO on the Arduino Uno when I am using assembly for programming?

**Background:** I was interested in practicing my assembly language skills on the Arduino (I thought it would be easier to turn LEDs on/off than to worry about console IO). From doing a [preliminary search](https://electronics.stackexchange.com/q/12750/17375), I have found that the AVR toolchain can be used to program the Arduino. Yet, I don't quite know how to find the corresponding registers for the IO pins.