NRF52811-QCAA-R datasheet(166/444 Pages) NORDIC

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Peripherals

The sample period and accumulation are configurable to match application requirements. The QDEC

provides the following:

• Decoding of digital waveform from off-chip quadrature encoder.

• Sample accumulation eliminating hard real-time requirements to be enforced on application.

• Optional input de-bounce filters.

• Optional LED output signal for optical encoders.

Mechanical to electrical

Mechanical

device

Quadrature decoder

SAMPLE

Quadrature Encoder

IO router

On-chip

Off-chip

ACC

ACCREAD

ACCDBL

ACCDBLREAD

Phase A

Phase B

LED

Figure 56: Quadrature decoder configuration

6.13.1 Sampling and decoding

The QDEC decodes the output from an incremental motion encoder by sampling the QDEC phase input

pins (A and B).

The off-chip quadrature encoder is an incremental motion encoder outputting two waveforms, phase

A and phase B. The two output waveforms are always 90 degrees out of phase, meaning that one

always changes level before the other. The direction of movement is indicated by which of these two

waveforms that changes level first. Invalid transitions may occur, that is when the two waveforms switch

simultaneously. This may occur if the wheel rotates too fast relative to the sample rate set for the decoder.

The QDEC decodes the output from the off-chip encoder by sampling the QDEC phase input pins (A and B)

at a fixed rate as specified in the SAMPLEPER register.

If the SAMPLEPER value needs to be changed, the QDEC shall be stopped using the STOP task. SAMPLEPER

can be then changed upon receiving the STOPPED event, and QDEC can be restarted using the START task.

Failing to do so may result in unpredictable behaviour.

4454_140 v1.0

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NRF52811-QCAA-R Datasheet(PDF) 166 Page - Nordic Semiconductor