Chapter 9

Counters

Non-Cumulative Buffered Edge Counting

Non-cumulative edge counting is similar to buffered (sample clock) edge counting. However, the counter resets after each active edge of the Sample Clock. You can route the Sample Clock to the Gate input of the counter.

Figure 9-5shows an example of non-cumulative buffered edge counting.

 

Counter

 

 

 

 

 

 

Sample Clock

Armed

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

(Sample on

 

 

 

 

 

 

 

 

 

Rising Edge)

 

 

 

 

 

 

 

 

 

SOURCE

 

 

 

 

 

 

 

 

 

Counter Value

0 1 2 1

2 3 1 2

3

1

 

 

 

 

 

 

 

 

 

 

 

 

2

2

 

2

Buffer

 

 

 

 

3

 

 

3

 

 

 

 

 

 

3

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Figure 9-5.Non-Cumulative Buffered Edge Counting

Notice that the first count interval begins when the counter is armed, which occurs before the first active edge on Gate.

Note that if you are using an external signal as the Source, at least one Source pulse should occur between each active edge of the Gate signal. This condition ensures that correct values are returned by the counter. If this condition is not met, consider using duplicate count prevention, described in the Duplicate Count Prevention section.

Controlling the Direction of Counting

In edge counting applications, the counter can count up or down. You can configure the counter to do the following:

•Always count up

•Always count down

•Count up when the Counter n B input is high; count down when it is low

For information about connecting counter signals, refer to the Default

Counter/Timer Pinouts section.