National Instruments 321645c-01 用户手册

Chapter 2

Function Reference — GPCTR_Set_Application

National Instruments Corporation

2-219

NI-DAQ FRM for PC Compatibles

Figure 2-15 shows one possible scenario of a counter used for

ND_SINGLE_PERIOD_MSR

after the following programming sequence:

GPCTR_Control(deviceNumber, gpctrNum, ND_RESET)

GPCTR_Set_Application(deviceNumber, gpctrNum,

ND_SINGLE_PERIOD_MSR)GPCTR_Set_Application

GPCTR_Control(deviceNumber, gpctrNum, ND_PROGRAM)

In Figure 2-15, the following behavior is present:

•

Gate is the signal present at the counter gate input.

•

Source is the signal present at the counter source input.

•

Count is the value you would read from the counter if you called the

GPCTR_Watch

function with entityID =

ND_COUNT

. The different numbers illustrate behavior at

different times.

•

Armed is the value you would read from the counter if you called the

GPCTR_Watch

function with entityID =

ND_ARMED

. The different values illustrate behavior at different

times.

Figure 2-15. Single Period Measurement

Use the

GPCTR_Watch

function with entityID =

ND_ARMED

to monitor the progress of the

counting process. This measurement completes when entityValue becomes

ND_NO

. When

the counter is no longer armed, you can retrieve the counted value by using

GPCTR_Watch

with entityID =

ND_COUNT

. You can do this as follows:

Create u32 variable counter_armed.

Create u32 variable counted_value.

repeat

{

GPCTR_Watch(deviceNumber, gpctrNumber, ND_ARMED, counter_armed)

}

YES

Gate

Source

Count

Armed

Measured

Interval