33FJ128GP708 datasheet(29/90 Pages) MICROCHIP

29 / 90 page

Preliminary

DS70155C-page 27

dsPIC33F

8.4

Quadrature Encoder Interface

(QEI) Module

Quadrature encoders (also referred to as incremental

encoders or optical encoders) are used in position and

speed

detection

rotating

motion

systems.

Quadrature encoders enable closed-loop control of

many motor control applications, such as Switched

Reluctance (SR) Motor and AC Induction Motor

(ACIM).

Typically, three outputs termed, Phase A, Phase B and

INDEX, provide information that can be decoded to

provide information on the movement of the motor

shaft, including distance and direction.

A quadrature decoder captures the phase signals and

index pulse and converts the information into a numeric

count of the position pulses. Generally, the count will

increment when the shaft is rotating one direction and

decrement when the shaft is rotating in the other

direction.

The QEI module (Figure 8-3) includes:

• Three input pins for two phase signals and index

pulse

• Programmable digital noise filters on inputs

• Quadrature decoder providing counter pulses and

count direction

• 16-bit up/down position counter

• Count direction status

• x2 and x4 count resolution

• Two modes of Position Counter Reset

• General Purpose16-Bit Timer/Counter mode

• Interrupts generated by QEI or counter events

FIGURE 8-3:

QUADRATURE ENCODER INTERFACE BLOCK DIAGRAM

16-Bit Up/Down Counter

Comparator/

Max Count Register

Quadrature

Programmable

Digital Filter

QEA

Programmable

Digital Filter

INDX

Up/Down

Existing Pin Logic

UPDN

Encoder

Programmable

Digital Filter

QEB

Interface Logic

QEIM<2:0>

Mode Select

(POSCNT)

(MAXCNT)

PCDOUT

QEIIF

Event

Flag

Reset

Equal

TCY

TQCS

TQCKPS<1:0>

1, 8, 64, 256

Prescaler

TQGATE

QEIM<2:0>

Synchronize

Det

Sleep Input

UPDN_SRC

QEICON<11>

Zero Detect

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