Справочник Пользователя для National Instruments 321645c-01

Chapter 2

Function Reference — GPCTR_Set_Application

NI-DAQ FRM for PC Compatibles

2-224

National Instruments Corporation

Figure 2-17. Single Triggered Pulse Width Generation Measurement

Use the

GPCTR_Watch

function with entityID =

ND_COUNT_AVAILABLE

to monitor the

progress of the counting process. This measurement completes when entityValue becomes

ND_YES

. After this is completed, you can retrieve the counted value by using

GPCTR_Watch

with entityID =

ND_COUNT

, as shown in the following example code:

Create u32 variable count_available.

Create u32 variable counted_value.

repeat

{

GPCTR_Watch(deviceNumber, gpctrNumber, ND_COUNT_AVAILABLE,

count_available)

}

until (count_available = ND_YES)

GPCTR_Watch(deviceNumber, gpctrNumber, ND_COUNT, counted_value)

To calculate the measured interval, multiply the counted value by the period corresponding to
the timebase you are using. For example, if your

ND_SOURCE

ND_INTERNAL_20_MHZ

, the

interval will be 1/(20 MHz) = 50 ns. If the

ND_COUNT

is 4 (Figure 2-15), the actual interval is

4 * 50 ns = 200 ns.

Note

The measured interval will correspond to the most recent pulse that arrived prior
to the invoking of

GPCTR_Watch

call with entityID set to

ND_COUNT_AVAILABLE

Caution

There should be source transitions between gate transitions in order for this
measurement to be correct.

Gate

Source

Count

Count
Available

Measured

Interval

YES

Trigger