But why then are you asking for code instead of just "material"? Andy have given you a lot of links to "material".

No need to worry about closed libraries. A closed library may stop you from getting access to printed material. But anything you need to know about a microcontroller in general, your specific microcontroller, about hardware in general, about algorithms, ... can be found on the net. But I'm not talking about turn-key solutions. I'm talking about reference documents with all instructions in the processor. Datasheets describing all peripherials in the processor and all registers. Design snippets showing how to initialize a port and control a LED. How to connect and control a transistor. How to use a serial port. How to ...

Everything is available for you. Google will find it. But it is individual snippets, and you must read and learn from more than one source to integrate into knowledge and into a program that you can turn in.

We are living in an Internet era - never complain that you can't get access to information. You can. The problem is that you can get access to too much information. But that is a problem that isn't too hard to live with.

Now, start working. And come back if you get stuck.