Some doubts about MCU

Hello~all,thanks for reading my post.I know that maybe my thread is far away for the subject of forum,but I know someone here is able enough to help me.

I’m so interesting in the electronics,especially in the programming or codec and receive by using IC. I met some troubles now .

Recently I bought a board that using transistor and Oscillator output in. It’s in a low price, I feel.And I make a research on it, The receive port is demodulating by PT4302.( this one),and then MCU will decode it.
Now my problem is : How to output the code by using the IO port of MCU?

What I can thought just pwm,but how to realize it exactly, I have no way.

Your help will be appreciated!

Use Virtualwire

// Per.