Index Pulse Example - Texas Instruments Concerto F28M35 Series Technical Reference Manual

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Introduction

Quadrature encoders from different manufacturers come with two forms of index pulse (gated index pulse

or ungated index pulse) as shown in

ungated configuration, the index edges are not necessarily coincident with A and B signals. The gated

index pulse is aligned to any of the four quadrature edges and width of the index pulse and can be equal

to a quarter, half, or full period of the quadrature signal.

(gated to A)

Some typical applications of shaft encoders include robotics and even computer input in the form of a

mouse. Inside your mouse you can see where the mouse ball spins a pair of axles (a left/right, and an

up/down axle). These axles are connected to optical shaft encoders that effectively tell the computer how

fast and in what direction the mouse is moving.

General Issues: Estimating velocity from a digital position sensor is a cost-effective strategy in motor

control. Two different first order approximations for velocity may be written as:

x ( k ) * x ( k * 1 )

t ( k ) * t ( k * 1 )

v(k): Velocity at time instant k

x(k): Position at time instant k

x(k-1): Position at time instant k-1

T: Fixed unit time or inverse of velocity calculation rate

ΔX: Incremental position movement in unit time

t(k): Time instant "k"

t(k-1): Time instant "k-1"

X: Fixed unit position

ΔT: Incremental time elapsed for unit position movement.

is the conventional approach to velocity estimation and it requires a time base to provide unit

time event for velocity calculation. Unit time is basically the inverse of the velocity calculation rate.

C28 Enhanced QEP (eQEP) Module

9-3. A nonstandard form of index pulse is ungated. In the

Figure 9-3. Index Pulse Example

SPRUH22I – April 2012 – Revised November 2019

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