An embedded project/product without a Universal Asynchrounous Receiver Transmiter (UART) interface is unimaginable. Even if the MCU is not talking to another serial device, you'll need it at-least during the development work to speak to your computer. UART also come in handy for firmware upgrade and enabling/disabling product features during it's lifetime. This probably one of the first interfaces you would want to include in your project.
So let's get started! As with the series, we will be using a Atmega32 for this tutorial, other AVRs should work the same way. Do do not forget to look at the datasheet once before trying out with other controllers.
Basics
I know you're getting your head around the acronym UART still, but do not worry it is simple. Don't know where the word Universal came from but, Asynchronous makes lot of sense.
Figure below shows the typical connection of a serial device with the MCU. There are basically Transmit(Tx) and Receive(Rx) lines and a common ground.
Now imagine we want to send some data as shown below:
