PIC18F2331 MICROCHIP [Microchip Technology], PIC18F2331 Datasheet - Page 172

• Manufacturer Part Number: PIC18F2331
• Description: 28/40/44-Pin Enhanced Flash Microcontrollers with nanoWatt Technology, High Performance PWM and A/D
• Manufacturer: MICROCHIP [Microchip Technology]

PIC18F2331/2431/4331/4431
16.2
The Quadrature Encoder Interface (QEI) decodes
speed and motion sensor information. It can be used in
any application that uses a quadrature encoder for
feedback. The interface implements these features:
• Three QEI inputs: two phase signals (QEA and
• Direction of movement detection with a direction
• 16-bit up/down position counter
• Standard and high-precision position tracking
• Two position update modes (x2 and x4)
• Velocity measurement with a programmable
• Position counter interrupt (IC2QEIF in the PIR3
• Velocity control interrupt (IC1IF in the PIR3
The QEI sub-module has three main components: the
QEI control logic block, the position counter and
velocity postscaler.
FIGURE 16-8:
DS39616B-page 170
CAP3/QEB
CAP2/QEA
CAP1/INDX
QEB) and one index signal (INDX)
change interrupt (IC3DRIF)
modes
postscaler for high-speed velocity measurement
register)
register)
Quadrature Encoder Interface
QEI BLOCK DIAGRAM
Filter
Filter
Filter
QEB
QEA
INDX
Direction change
QEI
Control
Logic
Velocity Event
Preliminary
Timer reset
Direction
Clock
The QEI control logic detects the leading edge on the
QEA or QEB phase input pins, and generates the count
pulse which is sent to the position counter logic. It also
samples the index input signal (INDX), and generates
the direction of rotation signal (up/down) and the veloc-
ity event signals.
The position counter acts as an integrator for tracking
distance traveled. The QEA and QEB input edges
serve as the stimulus to create the input clock which
advances the Position Counter Register (POSCNT).
The register is incremented on either the QEA input
edge, or the QEA and QEB input edges, depending on
the operating mode. It is reset either by a rollover on
match to the Period Register, MAXCNT, or on the exter-
nal index pulse input signal (INDX). An interrupt is gen-
erated on a reset of POSCNT if the position counter
interrupt is enabled.
The velocity postscaler down-samples the velocity
pulses used to increment the velocity counter by a
specified ratio. It essentially divides down the number
of velocity pulses to one output per so many input, pre-
serving the pulse width in the process.
A simplified block-diagram of the QEI module is shown
in Figure 16-8.
QEI Module
Set CHGIF
Postscaler
POSCNT/CAP2BUF
MAXCNT/CAP3BUF
Position Counter
Comparator
 2003 Microchip Technology Inc.
Set UP/DOWN
Set IC2QEIF
Reset on match
Velocity Capture
Reset Timer5
8
8
8
8
8