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Event System (EVSYS)

What is the Event System?

The Event System (EVSYS) is a peripheral found on AVR® microcontrollers (MCUs) that allows other on-chip peripherals to signal directly to each other independently of the Central Processing Unit (CPU). Through the Event System, an output of one peripheral is propagated to many other peripherals. This improves response time and reduces power consumption while enabling more complex system configurations.

How Does the Event System Work?

The Event System is split into multiple channels. Each channel can have a single event generator and multiple event users. Since some peripherals operate asynchronously while others are synchronized to the peripheral clock, the Event System contains two subchannels for each type of peripheral. To make both types of peripherals compatible, the event system synchronizes asynchronous events for the synchronous peripherals. 

Event Channel Diagram

Types of Events

There are two types of events: pulsed output and level output. A pulsed output is only active for a single clock cycle whereas a level output is active for multiple clock cycles. A few examples of peripherals and their outputs are shown below.

Peripheral Description Output
Configurable Custom Logic (CCL) - LUT Output of the Look-Up Table (LUT) function Asynchronous Level
Analog Comparator (AC) - OUT Output of the Analog Comparator Asynchronous Level
Serial Peripheral Interface (SPI) - Clock Host mode clock from the SPI peripheral Synchronous Level
Analog-to-Digital Converter (ADC) - Result Ready Pulsed output that is generated when the ADC has a result ready Synchronous Pulse
Timer/Counter A (TCA) - Overflow Pulsed output from the timer overflow Synchronous Pulse

Note: The table above is not exhaustive. Other peripheral connections and outputs are available.  

8-bit Microcontrollers with Event System

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Similar Devices

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Documentation

Title
Interfacing Quadrature Encoder Using CCL with TCA and TCB Download
Using Event System on ATtiny817 Download
AN2451 - Getting Started with Core Independent Peripherals on AVR Download

Getting STARTed with AVR® MCUs

Episode 6: Trigger Conversions on Event for ADC in Window Comparator Mode