I am working on some project Where I have to deal with uc ATxmega128A1 , But being a beginner to a ucontrollers I want to know what is this channel event system regarding ucs. I have referred a link http://www.atmel.com/Images/doc8071.pdf but not getting it.
The traditional way to do things the channel system can do is to use interrupts.
In the interrupt model, the CPU runs the code starting with main(), and continues usually with some loop. When an particular event occurs, such as a button being pressed, the CPU is "interrupted". The current processing is stopped, some registers are saved, and the execution jumps to some code pointed to by an interrupt vector called an interrupt handler. This code usually has instructions to save register values, and this is added automatically by the compiler.
When the interrupting code is finished, the CPU restores the values that the registers previously had and execution jumps back to the point in the main code where it was interrupted.
But this approach takes valuable CPU cycles. And some interrupt handlers don't do very much expect trigger some peripheral to take an action. Wouldn't it be great it these kinds of interrupt handlers could be avoided and have the mC have the peripherals talk directly to each other without pausing the CPU?
This is what the event channel system does. It allows peripherals to trigger each other directly without involving the CPU. The CPU continues to execute instructions while the channel system operates in parallel. This doesn't mean you can replace all interrupt handlers, though. If complicated processing is involved, you still need a handler to act. But the channel system does allow you to avoid using very simple interrupt handlers.
The paper you reference describes this in a little more detail (but assumes a lot of knowledge on the reader's part). You have to read the actual datasheet of your mC to find the exact details.