Filter
Top Products
Scan IF Operation
24-34 Scan IF
Figure 24−20. Quadrature Decoding State Diagram
00
10
11
01
00
10
11
01
Correct State Transitions Erroneous State Transitions
+1−1
To transfer the state encoding into counts it is necessary to decide what
fraction of the rotation should be counted and on what state transitions. In this
example only full rotations will be counted on the transition from state 00 to 01
or 10 using a 180° disk with the sensors 90° apart. All the possible state
transitions can be put into a table and this table can be translated into the
corresponding state table entries for the processing state machine as shown
in Table 24−8.
Table 24−8.Quadrature Decoding PSM Table
Previous Current Movement
State Table Entry
Quad. Quad.
Q6
Q2 Q1 Q3 Q0
Pair Pair
Error
−1 +1 Current
Quad.
Pair
Byte
Code
00 00 No Rotation 0 0 0 0 0 000h
00 01 Turns right, +1 0 0 1 0 1 003h
00 10 Turns left, −101 0 1 0 00Ch
00 11 Error 1 0 0 1 1 049h
01 00 Turns left 0 0 0 0 0 000h
01 01 No rotation 0 0 0 0 1 001h
01 10 Error 1 0 0 1 0 048h
01 11 Turns right 0 0 0 1 1 009h
10 00 Turns right 0 0 0 0 0 000h
10 01 Error 1 0 0 0 1 041h
10 10 No rotation 0
0 0 1 0 008h
10 11 Turns left 0 0 0 1 1 009h
11 00 Error 1 0 0 0 0 040h
11 01 Turns left 0 0 0 0 1 001h
11 10 Turns right 0 0 0 1 0 008h
11 11 No rotation 0 0 0 1 1 009h