Specifications

Mode 20: Quadrature Counter
Purpose
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
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
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.
Functional Block Diagram
The diagram below shows HSIO functionality in Mode 20. When the lower byte of HSIO
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
B signal. X2 is dedicated to reset the counter to zero value when energized.
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,
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
edge precedes Phase A’s rising edge (indicates counter-clockwise motion), the counter counts
DOWN.
DL05 Micro PLC User Manual, 6th Edition, Rev. C
E–18
Appendix E: High-speed Input and Pulse Output Features
1
2
3
D
E
6
7
8
9
10
11
1
1
14
A
B
C
D
90˚ phase shift
Phase A
Phase B
Leading Edge Signal
Phase A
Phase B
Leading Edge Signal
Clockwise sequence
Counterclockwise sequence
one cycle
Input Circuit
CPU
PLC
DL05
Y0, Y1
X3 - X7
Y2 - Y5
V-memory
V7633 0020
Mode select
I/O data
HSIO
COUNTER
Phase
A
Phase
B
X2
Reset
X1
Output Circuit
X0