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2.1 EQEP Inputs

2.2 Functional Description

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Description

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.

• eQEPI: 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.

The eQEP peripheral contains the following major functional units (as shown in Figure 4 ):

• 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)

SPRUG05A – August 2008 – Revised December 2008 Enhanced QEP (eQEP) Module 11

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