Digi NS9215 - Manual (Page 146)

S Y S T E M C O N T R O L M O D U L E
How the quadrature decoder/counter works
146 Hardware Reference NS9215
A quadrature decoder/counter module performs these tasks at real time speed and
interrupts the CPU at the predetermined conditions.
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
H o w t h e q u a d r a t u r e d e c o d e r / c o u n t e r w o r k s
Provides input
signals
A quadrature encoder provides a pair of signals (in-phase and quad-phase) with
opposite polarities and a 90-degree phase shift. Decode these signals to create an
algorithm to determine the direction, speed, and position of a motion wheel.
Input signals
Quadrature
encoding truth
table
Legend:
NC — No change
CW — Clockwise
CCW — Counter clockwise
Err — Error
00 01 10 11 00 01 10 11 00 00 10 01 01 00 11
Clockwise
Counter
Clockwise
I:Q 00 01 10 11
00 NC CW CCW Err
01 CCW NC Err CW
10 CW Err NC CCW
11 Err CCW CW NC