LM3S1620 Datasheet, PDF (418/485 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 Stellaris^® quadrature encoder interface (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^® quadrature encoder has the following features:
■ Position integrator that tracks the encoder position
■ Velocity capture using built-in timer
■ Interrupt generation on:
– Index pulse
– Velocity-timer expiration
– Direction change
– Quadrature error detection
Block Diagram
Figure 17-1 on page 418 provides a block diagram of a Stellaris^® QEI module.
Figure 17-1. QEI Block Diagram
Control & Status
QEICTL
QEISTAT
QEILOAD
Velocity Timer
QEITIME
PhA
PhB
IDX
Velocity
Predivider
clk
Quadrature
Encoder dir
Velocity Accumulator
QEICOUNT
QEISPEED
QEIMAXPOS
Position Integrator
QEIPOS
QEIINTEN
Interrupt Control
QEIRIS
QEIISC
Interrupt
418
September 02, 2007
Preliminary