XMEGAD datasheet(49/309 Pages) ATMEL

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8210B–AVR–04/10

XMEGA D

Figure 5-4 shows typical quadrature signals from a rotary encoder. The signals QDPH0 and

QDPH90 are the two quadrature signals. When QDPH90 leads QDPH0, the rotation is defined

as positive or forward. When QDPH0 leads QDPH90, the rotation is defined as negative, or

reverse. The concatenation of the two phase signals is called the quadrature state or the phase

state.

In order to know the absolute rotary displacement a third index signal (QDINDX) can be used.

This gives an indication once per revolution.

5.7.2

QDEC Setup

For a full QDEC setup the following is required:

• I/O port pins - quadrature signal input

• The Event System - quadrature decoding

• A Timer/Counter - up, down and optional index count

The following procedure should be used for QDEC setup:

• Choose two successive pins on a port as QDEC phase inputs.

• Set pin direction for QDPH0 and QDPH90 as input.

• Set pin configuration for QDPH0 and QDPH90 to low level sense.

• Select QDPH0 pin as multiplexer input for an event channel, n.

• Enable quadrature decoding and digital filtering in the Event Channel.

• Optional:

Setup QDEC index (QINDX).

Select a third pin for QINDX input.

Set pin direction for QINDX as input.

Set pin configuration for QINDX to sense both edges.

Select QINDX as multiplexer input for Event Channel n+1

Set the Quadrature Index Enable bit in Event Channel n+1.

Select the Index Recognition mode for Event Channel n+1.

• Set quadrature decoding as event action for a Timer/Counter.

• Select Event Channel n as event source the Timer/Counter.

• Set the period register of the Timer/Counter to ('line count' * 4 - 1). (The line count of the

quadrature encoder).

• Enable the Timer/Counter by setting CLKSEL to a CLKSEL_DIV1.

The angle of a quadrature encoder attached to QDPH0, QDPH90 (and QINDX) can now be read

directly from the Timer/Counter Count register. If the Count register is different from BOTTOM

when the index is recognized, the Timer/Counter error flag is set. Similarly the error flag is set if

the position counter passes BOTTOM without the recognition of the index.

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