Matrox Rapixo CL Pro, Установка и справочник по оборудованию, Страница: 52 / 96

52 Chapter 4: Matrox Rapixo CL Pro hardware reference
Quadrature decoder
Matrox Rapixo CL Pro features 4 quadrature decoders. They are used to decode
quadrature input received from rotary or linear encoders with a quadrature output.
A rotary encoder is a device that provides information about the position and
direction of a rotating shaft (for example, that of a conveyor belt); a linear encoder
is a device that provides information about the position and direction of a moving
sensor along a scale. Encoders with quadrature output transmit a two-bit code
(also known as Gray code) on two pairs of LVDS wires for each change in position
of the rotating shaft, or of the sensor along the scale. For a given direction, the
encoder outputs the code in a precise sequence (either 00 - 01 - 11 - 10 or 00 -
10 - 11 - 01, depending on how the encoder is attached. If the rotating shaft, or
sensor moving along the scale, changes direction, the encoder transmits the Gray
code in the reverse sequence (00 - 10 - 11 - 01 or 00 - 01- 11 - 10, respectively).
Upon decoding a Gray code, the quadrature decoder increments or decrements
its 32-bit internal counter, depending on the direction of movement. You can
configure which Gray code sequence represents forward movement and
increments the counter; the reverse Gray code sequence will then represent the
backward direction and decrement the counter. You can specify the direction of
movement occurring when the Gray code sequence is 00 - 01 - 11 - 10, using
MdigControl() with M_ROTARY_ENCODER_DIRECTION.
The quadrature decoder supports encoder frequencies of up to 50 MHz. The
LVDS receivers of the Matrox Rapixo CL Pro board support an input voltage from
-4 V to +5 V on either LVDS signal, and a maximum differential of 3 V between
the two LVDS signals.
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Note that an external source must be used to power the rotary/linear encoder
(for example, your computer’s 5 V power source).
You can configure the quadrature decoder’s settings, using the MIL-Lite function
MdigControl() with M_ROTARY_ENCODER... , or by modifying the DCF file
with Matrox Intellicam.