LM3S1968 Datasheet, PDF (602/709 Pages) List of Unclassifed Manufacturers – Microcontroller

Quadrature Encoder Interface (QEI)
17
17.1
Quadrature Encoder Interface (QEI)
A quadrature encoder, also known as a 2-channel incremental encoder, converts linear displacement
into a pulse signal. By monitoring both the number of pulses and the relative phase of the two signals,
you can track the position, direction of rotation, and speed. In addition, a third channel, or index
signal, can be used to reset the position counter.
The LM3S1968 microcontroller includes two quadrature encoder interface (QEI) modules. Each
QEI module interprets the code produced by a quadrature encoder wheel to integrate position over
time and determine direction of rotation. In addition, it can capture a running estimate of the velocity
of the encoder wheel.
Each Stellaris^® quadrature encoder has the following features:
■ Two QEI modules, each with the following features:
■ Position integrator that tracks the encoder position
■ Velocity capture using built-in timer
■ The input frequency of the QEI inputs may be as high as 1/4 of the processor frequency (for
example, 12.5 MHz for a 50-MHz system)
■ Interrupt generation on:
– Index pulse
– Velocity-timer expiration
– Direction change
– Quadrature error detection
Block Diagram
Figure 17-1 on page 603 provides a block diagram of a Stellaris QEI module.
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July 15, 2014
Texas Instruments-Production Data