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48 Chapter 2: Getting started with your Matrox 4Sight GPm unit
Rotary decoder
The Matrox 4Sight GPm unit features two rotary decoders (quadrature decoders).
A rotary decoder is used to decode quadrature input received from a rotary encoder
with 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). The encoder outputs a two-bit code (also known as Gray code) on two wires
for each change in position of the rotating shaft; for a given direction of the rotating
shaft, the rotary encoder outputs the code in a precise sequence (either 00 - 01 -
11 - 10 or 00 - 10 - 11 - 01, depending on how the rotary encoder is attached to
the rotating shaft). If the rotating shaft changes direction, the rotary encoder
transmits the Gray code in the reverse sequence (00 - 10 - 11 - 01 or 00 - 01- 11
- 10, respectively).
Your Matrox 4Sight GPm can receive quadrature input on any of its TTL auxiliary
input signals. For information, refer to the Using quadrature input from a rotary
encoder section in the MIL online help.
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