Product Specs

36 QDEC — Quadrature decoder
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349
Note that when when the debounce filters are enabled, displacements reported by the QDEC peripheral are
delayed by one SAMPLEPER period.
36.4 Accumulators
The quadrature decoder contains two accumulator registers, ACC and ACCDBL, that accumulate
respectively valid motion sample values and the number of detected invalid samples (double transitions).
The ACC register will accumulate all valid values (1/-1) written to the SAMPLE register. This can be useful
for preventing hard real-time requirements from being enforced on the application. When using the ACC
register the application does not need to read every single sample from the SAMPLE register, but can
instead fetch the ACC register whenever it fits the application. The ACC register will always hold the relative
movement of the external mechanical device since the previous clearing of the ACC register. Sample values
indicating a double transition (2) will not be accumulated in the ACC register.
An ACCOF event will be generated if the ACC receives a SAMPLE value that would cause the register to
overflow or underflow. Any SAMPLE value that would cause an ACC overflow or underflow will be discarded,
but any samples not causing the ACC to overflow or underflow will still be accepted.
The accumulator ACCDBL accumulates the number of detected double transitions since the previous
clearing of the ACCDBL register.
The ACC and ACCDBL registers can be cleared by the READCLRACC and subsequently read using the
ACCREAD and ACCDBLREAD registers.
The ACC register can be separately cleared by the RDCLRACC and subsequently read using the ACCREAD
registers.
The ACCDBL register can be separately cleared by the RDCLRDBL and subsequently read using the
ACCDBLREAD registers.
The REPORTPER register allows automating the capture of several samples before it can send out a
REPORTRDY event in case a non-null displacement has been captured and accumulated, and a DBLRDY
event in case one or more double-displacements have been captured and accumulated. The REPORTPER
field in this register selects after how many samples the accumulators contents are evaluated to send (or not)
REPORTRDY and DBLRDY events.
Using the RDCLRACC task (manually sent upon receiving the event, or using the DBLRDY_RDCLRACC
shortcut), ACCREAD can then be read.
In case at least one double transition has been captured and accumulated, a DBLRDY event is sent. Using
the RDCLRDBL task (manually sent upon receiving the event, or using the DBLRDY_RDCLRDBL shortcut),
ACCDBLREAD can then be read.
36.5 Output/input pins
The QDEC uses a three-pin interface to the off-chip quadrature encoder.
These pins will be acquired when the QDEC is enabled in the ENABLE register. The pins acquired by the
QDEC cannot be written by the CPU, but they can still be read by the CPU.
The pin numbers to be used for the QDEC are selected using the PSEL.n registers.
36.6 Pin configuration
The Phase A, Phase B, and LED signals are mapped to physical pins according to the configuration
specified in the PSEL.A, PSEL.B, and PSEL.LED registers respectively.
If the CONNECT field value 'Disconnected' is specified in any of these registers, the associated signal
will not be connected to any physical pin. The PSEL.A, PSEL.B, and PSEL.LED registers and their
configurations are only used as long as the QDEC is enabled, and retained only as long as the device is in