LPC1766_0.02
© NXP B.V. 2008. All rights reserved.
Objective data sheet
Rev. 00.02 — 12 August 2008
27 of 70
NXP Semiconductors
LPC1766
Fast communication chip
PWM to immediately release all motor drive outputs. At the same time, the motor control
PWM is highly configurable for other generalized timing, counting, capture, and compare
applications.
7.24 Quadrature Encoder Interface (QEI)
A quadrature encoder, also known as a 2-channel incremental encoder, converts angular
displacement into two pulse signals. By monitoring both the number of pulses and the
relative phase of the two signals, the user can track the position, direction of rotation, and
velocity. In addition, a third channel, or index signal, can be used to reset the position
counter. The quadrature encoder interface decodes the digital pulses from a quadrature
encoder wheel to integrate position over time and determine direction of rotation. In
addition, the QEI can capture the velocity of the encoder wheel.
7.24.1 Features
• Tracks encoder position.
• Increments/decrements depending on direction.
• Programmable for 2x or 4x position counting.
• Velocity capture using built-in timer.
• Velocity compare function with “less than” interrupt.
• Uses 32-bit registers for position and velocity.
• Three position compare registers with interrupts.
• Index counter for revolution counting.
• Index compare register with interrupts.
• Can combine index and position interrupts to produce an interrupt for whole and
partial revolution displacement.
• Digital filter with programmable delays for encoder input signals.
• Can accept decoded signal inputs (clk and direction).
• Connected to APB.
7.25 Repetitive Interrupt (RI) timer
The repetitive interrupt timer provides a free-running 32-bit counter which is compared to
a selectable value, generating an interrupt when a match occurs. Any bits of the
timer/compare can be masked such that they do not contribute to the match detection.
The repetitive interrupt timer can be used to create an interrupt that repeats at
predetermined intervals.
7.25.1 Features
• 32-bit counter running from PCLK. Counter can be free-running or be reset by a
generated interrupt.
• 32-bit compare value.
• 32-bit compare mask. An interrupt is generated when the counter value equals the
compare value, after masking. This allows for combinations not possible with a simple
compare.
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