Chapter 9

Counters

Figure 9-15shows a quadrature cycle and the resulting increments and decrements for X1 encoding. When channel A leads channel B, the increment occurs on the rising edge of channel A. When channel B leads channel A, the decrement occurs on the falling edge of channel A.

Ch A

Ch B

Counter Value 5

6

7

7

6

5

Figure 9-15. X1 Encoding

X2 Encoding

The same behavior holds for X2 encoding except the counter increments or decrements on each edge of channel A, depending on which channel leads the other. Each cycle results in two increments or decrements, as shown in Figure 9-16.

Ch A

Ch B

Counter Value 5

6

7

8

9

9

Figure 9-16. X2 Encoding

X4 Encoding

8

7 6 5

Similarly, the counter increments or decrements on each edge of channels A and B for X4 encoding. Whether the counter increments or decrements depends on which channel leads the other. Each cycle results in four increments or decrements, as shown in Figure 9-17.

Ch A

Ch B

Counter Value 5

6 7 8 9 10 11 12 13 13 12 11 10 9 8 7 6

5

Figure 9-17. X4 Encoding