Mode 20: Quadrature Counter; Purpose; Functional Block Diagram; Quadrature Encoder Signals - Automation Direct DL05 User Manual

Appendix E: High-speed Input and Pulse Output Features

Mode 20: Quadrature Counter

1

Purpose

2
The counter in the HSIO circuit can count two quadrature signal pulses instead of a single
pulse train (mode 10 operation). Quadrature signals are commonly generated from
3
incremental encoders, which may be rotary or linear. The quadrature counter has two ranges
from 0 to 99999999 or -8388608 to 8388607. Using CT76 and CT77, the quadrature
counter can count at up to a 5 kHz rate. Unlike Mode 10 operation, Mode 20 operation can
D
count UP or DOWN, but does not feature automated preset values or "interrupt on external
reset" capability. However, you have the standard ladder instruction preset of CT76.
E

Functional Block Diagram

The diagram below shows HSIO functionality in Mode 20. When the lower byte of HSIO
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Mode register V7633 contains a BCD "20", the quadrature counter in the HSIO circuit is
enabled. Input X0 is dedicated to the Phase A quadrature signal, and input X1 receives Phase
7
B signal. X2 is dedicated to reset the counter to zero value when energized.
8
9
10
11
1

Quadrature Encoder Signals

Quadrature encoder signals contain position and direction information, while their frequency
represents speed of motion. Phase A and B signals shown below are phase-shifted 90 degrees,
1
thus the quadrature name. When the rising edge of Phase A precedes Phase B's leading edge
(indicates clockwise motion by convention), the HSIO counter counts UP. If Phase B's rising
14
edge precedes Phase A's rising edge (indicates counter-clockwise motion), the counter counts
DOWN.
A
B
C
D
E–18
DL05 Micro PLC User Manual, 6th Edition, Rev. A
DL05
PLC
COUNTER
Phase Phase
A B
X0 X1
Leading Edge Signal
Clockwise sequence
Phase A
Phase B
Counterclockwise sequence
Phase A
Phase B
Leading Edge Signal
Output Circuit
Y0, Y1
HSIO
I/O data
Mode select
Reset
X2
Input Circuit
90˚ phase shift
one cycle
Y2 - Y5
CPU
V-memory
V7633 0020
X3 - X7