Actually the best place to start is the simple LED Blink project. It is the "Hello world" of embedded systems ;-)

Project definition is simple: Get an LED to blink on a certain port pin.

First use software loops to control the blink rate. It's a good place to learn interrupts too, as you can progress to using timers to control the blink rate. Then maybe connect a switch to turn the blinking on and off.... Progress in simple steps like this is the best way to learn. RS-232 communication is a good project when you've mastered the concept of interrupts and timers, but starting off with it may be a bit heavy.

Another good way to learn is to look at existing projects (complete with source code and circuit diagrams) and get them to work as described. Getting a ready-made project to work itself is a learning experience!

kundi