19 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 LM3S6G65 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.
The Stellaris
®
LM3S6G65 microcontroller includes two QEI modules providing control of two motors
at the same time with the following features:
■ Position integrator that tracks the encoder position
■ Programmable noise filter on the inputs
■ 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
19.1 Block Diagram
Figure 19-1 on page 901 provides a block diagram of a Stellaris QEI module.
July 24, 2012900
Texas Instruments-Production Data
Quadrature Encoder Interface (QEI)
OBSOLETE: TI has discontinued production of this device.
