Enhanced Quadrature Encoder Pulse (eQEP) Module
15.4.2 Functional Description
This section provides the eQEP inputs and functional description.
NOTE:
Multiple identical eQEP modules can be contained in a system. The number of modules is
device-dependent and is based on target application needs. In this document, the letter x
within a signal or module name is used to indicate a generic eQEP instance on a device.
15.4.2.1 EQEP Inputs
The eQEP inputs include two pins for quadrature-clock mode or direction-count mode, an index (or 0
marker), and a strobe input.
•
QEPA/XCLK and QEPB/XDIR: These two pins can be used in quadrature-clock mode or direction-
count mode.
–
Quadrature-clock Mode: The eQEP encoders provide two square wave signals (A and B) 90
electrical degrees out of phase whose phase relationship is used to determine the direction of
rotation of the input shaft and number of eQEP pulses from the index position to derive the relative
position information. For forward or clockwise rotation, QEPA signal leads QEPB signal and vice
versa. The quadrature decoder uses these two inputs to generate quadrature-clock and direction
signals.
–
Direction-count Mode: In direction-count mode, direction and clock signals are provided directly
from the external source. Some position encoders have this type of output instead of quadrature
output. The QEPA pin provides the clock input and the QEPB pin provides the direction input.
•
QEPI: Index or Zero Marker: The eQEP encoder uses an index signal to assign an absolute start
position from which position information is incrementally encoded using quadrature pulses. This pin is
connected to the index output of the eQEP encoder to optionally reset the position counter for each
revolution. This signal can be used to initialize or latch the position counter on the occurrence of a
desired event on the index pin.
•
QEPS: Strobe Input: This general-purpose strobe signal can initialize or latch the position counter on
the occurrence of a desired event on the strobe pin. This signal is typically connected to a sensor or
limit switch to notify that the motor has reached a defined position.
15.4.2.2 Functional Description
The eQEP peripheral contains the following major functional units (as shown in
•
Programmable input qualification for each pin (part of the GPIO MUX)
•
Quadrature decoder unit (QDU)
•
Position counter and control unit for position measurement (PCCU)
•
Quadrature edge-capture unit for low-speed measurement (QCAP)
•
Unit time base for speed/frequency measurement (UTIME)
•
Watchdog timer for detecting stalls (QWDOG)
1653
SPRUH73H – October 2011 – Revised April 2013
Pulse-Width Modulation Subsystem (PWMSS)
Copyright © 2011–2013, Texas Instruments Incorporated