Chapter 9

Counters

The counter counts the number of edges on the Source input while the Gate input remains active. On each trailing edge of the Gate signal, the counter stores the count in a hardware save register. A USB Signal Stream transfers the stored values to host memory.

Figure 9-7shows an example of a buffered pulse-width measurement.

GATE

 

 

 

 

 

 

SOURCE

 

 

 

 

 

 

COUNTER VALUE

0

1

2

3

1

2

 

 

 

 

3

 

3

BUFFER

 

 

 

3

 

2

 

 

 

 

2

 

 

 

 

 

Figure 9-7.Buffered Pulse-Width Measurement

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.

For information about connecting counter signals, refer to the Default

Counter/Timer Pinouts section.

Period Measurement

In period measurements, the counter measures a period on its Gate input signal after the counter is armed. You can configure the counter to measure the period between two rising edges or two falling edges of the Gate input signal.

You can route an internal or external periodic clock signal (with a known period) to the Source input of the counter. The counter counts the number of rising (or falling) edges occurring on the Source input between the two active edges of the Gate signal.

You can calculate the period of the Gate input by multiplying the period of the Source signal by the number of edges returned by the counter.