NRF52820-QDAA-R datasheet(148/437 Pages) NORDIC

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Peripherals

6.11 QDEC — Quadrature decoder

The Quadrature decoder (QDEC) provides buffered decoding of quadrature-encoded sensor signals. It is

suitable for mechanical and optical sensors.

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 45: Quadrature decoder configuration

6.11.1 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 the waveform that changes level

first. Invalid transitions may occur, meaning the two waveforms simultaneously switch. 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.

4463_156 v1.0

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NRF52820-QDAA-R Datasheet(PDF) 148 Page - Nordic Semiconductor