LM3S8G62 Datasheet, PDF (950/1096 Pages) Texas Instruments – Stellaris® LM3S8G62 Microcontroller

OBSOLETE: TI has discontinued production of this device.
Quadrature Encoder Interface (QEI)
20
20.1
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 LM3S8G62 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^® LM3S8G62 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
Block Diagram
Figure 20-1 on page 951 provides a block diagram of a Stellaris QEI module.
950
July 24, 2012
Texas Instruments-Production Data