Texas TMS320x2823x, Reference Manual

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1 Introduction
QEPA
QEPB
QEPI
Reference Guide
SPRUG05A – August 2008 – Revised December 2008
Enhanced QEP (eQEP) Module
The enhanced quadrature encoder pulse (eQEP) module is used for direct interface with a linear or rotary
incremental encoder to get position, direction, and speed information from a rotating machine for use in a
high-performance motion and position-control system.
A single track of slots patterns the periphery of an incremental encoder disk, as shown in Figure 1 . These
slots create an alternating pattern of dark and light lines. The disk count is defined as the number of
dark/light line pairs that occur per revolution (lines per revolution). As a rule, a second track is added to
generate a signal that occurs once per revolution (index signal: QEPI), which can be used to indicate an
absolute position. Encoder manufacturers identify the index pulse using different terms such as index,
marker, home position, and zero reference
Figure 1. Optical Encoder Disk
To derive direction information, the lines on the disk are read out by two different photo-elements that
"look" at the disk pattern with a mechanical shift of 1/4 the pitch of a line pair between them. This shift is
realized with a reticle or mask that restricts the view of the photo-element to the desired part of the disk
lines. As the disk rotates, the two photo-elements generate signals that are shifted 90 out of phase from
each other. These are commonly called the quadrature QEPA and QEPB signals. The clockwise direction
for most encoders is defined as the QEPA channel going positive before the QEPB channel and vise
versa as shown in
Figure 2 .
Enhanced QEP (eQEP) Module 8 SPRUG05A – August 2008 – Revised December 2008
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