Product Specs

36 QDEC — Quadrature decoder
Page
347
Quadrature decoder
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ACCDBL
ACCDBLREAD
On-chip
Off-chip
Phase A
Quadrature Encoder
Mechanical
device
LED
Phase B
IO router
Mechanical to electrical
36 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.
Figure 97: Quadrature decoder configuration
36.1 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.
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SAMPLE
ACC
ACCREAD