XMEGAD datasheet(48/309 Pages) ATMEL

48 / 309 page

8210B–AVR–04/10

XMEGA D

datasheet for each peripheral, but unless stated, an event lasts for one peripheral clock cycle

only.

It takes maximum two clock cycles from an event is generated until the event actions in other

peripherals is triggered. It takes one clock cycle from the event happens until it is registered by

the event routing network on the first positive clock edge. It takes an additional clock cycle to

route the event through the event channel to the event user.

5.6

Filtering

Each event channel includes a digital filter. When this is enabled for an event channel, an event

must be sampled with the same value for configurable number of system clock cycles before it is

accepted. This is primarily intended for pin change events.

5.7

Quadrature Decoder

The Event System includes one Quadrature Decoder (QDEC). This enables the Event System

to decode quadrature input on I/O pins, and send data events that a Timer/Counter can decode

to trigger the appropriate event action: count up, count down or index/reset. Table 5-2 on page

48 summarizes which quadrature decoder data events are available, how they are decoded, and

how they can be generated. The QDEC and related features, control and status register are

available for event channel 0.

5.7.1

Quadrature Operation

A quadrature signal is characterized by having two square waves phase shifted 90 degrees rela-

tive to each other. Rotational movement can be measured by counting the edges of the two

waveforms. The phase relationship between the two square waves determines the direction of

rotation.

Figure 5-4.

Quadrature signals from a rotary encoder

Table 5-2.

Quadrature Decoder Data Events

STROBE

DATA

Data Event User

Signaling Event User

No Event

Index/Reset

No Event

Count Down

Signaling Event

Count Up

Signaling Event

QDPH0

QDPH90

QDINDX

Forward Direction

Backward

Direction

1 cycle / 4 states

QDPH0

QDPH90

QDINDX

XMEGAD Datasheet(PDF) 48 Page - ATMEL Corporation

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