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Chapter 2

Function Reference — GPCTR_Set_Application

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 National Instruments Corporation

2-235

NI-DAQ FRM for PC Compatibles

In Figure 2-23, 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.

•

Output is the signal present at the counter output.

Figure 2-23.  Frequency Shift Keying

Use the 

GPCTR_Control

 function with action = 

ND_RESET

 to stop the pulse generation.

Typically, you will find modifying the following parameters through the 

GPCTR_Change_Parameter

 function useful when the counter application is 

ND_FSK

. 

You can change the following:

•

ND_COUNT_1

, 

ND_COUNT_2

, 

ND_COUNT_3

, and 

ND_COUNT_4

 to any value between 

2 and  2

24

 – 1. The defaults are given for illustrative purposes only. 

•

ND_SOURCE

 to 

ND_INTERNAL_100_KHZ

. With this timebase, you can generate pulses 

with a delay and length between 20 µs and 160 s. The timing resolution will be lower than 
if you are using the 

ND_INTERNAL_20_MHZ

 timebase. 

•

ND_GATE

 to any legal value listed in the 

GPCTR_Change_Parameter

 function 

description. 

You can use the 

GPCTR_Change_Parameter

 function after calling 

GPCTR_Set_Application

 and before calling 

GPCTR_Control

 with action = 

ND_PROGRAM

 

or 

ND_PREPARE

. 

To provide your timebase, connect your timebase source to one of the PFI pins on the I/O 
connector and change 

ND_SOURCE

 and 

ND_SOURCE_POLARITY

 to the appropriate values. 

You also can configure the other general-purpose counter for 

ND_FSK

, and set 

ND_SOURCE

 of 

this counter to 

ND_OTHER_GPCTR_TC

 to generate pulses with delays and intervals longer than 

160 s. 

ND_BUFFERED_EVENT_CNT

In this application, the counter is used for continuous counting of events. By default, the 
counted events are low-to-high transitions on the line given in Table 2-21. Counts present at 
specified events of the signal present at the gate are saved in a buffer. By default, those events 

Source

Output

2

1

3

4

5

6

2

1

2

1

3

2

1

3

2

1

4

3

2

1

Gate