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Introduction
1568
SLAU723A – October 2017 – Revised October 2018
Copyright © 2017–2018, Texas Instruments Incorporated
Quadrature Encoder Interface (QEI)
24.1 Introduction
The 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 MSP432E4 microcontroller includes one QEI module 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 system frequency (for example,
30 MHz for a 120-MHz system)
•
Interrupt generation on:
–
Index pulse
–
Velocity-timer expiration
–
Direction change
–
Quadrature error detection
24.2 Block Diagram
shows the internal block diagram of a QEI module. The PhA and PhB inputs shown in
are the internal signals that enter the Quadrature Encoder after the external signals, PhAn
and PhBn, have passed through inversion and swapping logic, shown in
. The QEI module has
the option of inverting and/or swapping the incoming signals.
NOTE:
Any references in this chapter to PhA and PhB refer to the internal PhA and PhB inputs that
enter the Quadrature Encoder after the external signals, PhAn and PhBn, have passed
through inversion and swapping logic that is enabled through the QEI Control (QEICTL)
register.