National Instruments 321645c-01 用户手册

Chapter 2

Function Reference — GPCTR_Change_Parameter

NI-DAQ FRM for PC Compatibles

2-206

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 National Instruments Corporation

ND_COUNT_1

, 

ND_COUNT_2

, 

ND_COUNT_3

, 

ND_COUNT_4

The general-purpose counter uses these numbers for pulse width specifications when the 
counter is configured for one of the simple pulse and pulse train generation applications. For 
example, when you use the counter for FSK, 

ND_COUNT_1

 and

 

ND_COUNT_2

 

specify the 

duration of low and high output states for one gate state and 

ND_COUNT_3

 and 

ND_COUNT_4

 

specify them for the other gate state. Corresponding legal values for paramValue are shown 
in Table 2-28.

For the 6602 devices, you can call 

GPCTR_Change_Parameter 

with 

paramID = 

ND_COUNT_1

 

or 

ND_COUNT_2

 

after arming the counter with a 

GPCTR_Control

 

call. By using this, you can modify the duty cycle of a pulse-train whose generation was 
started by the 

GPCTR_Set_Application 

call with application = 

ND_PULSE_TRAIN_GNR

. 

You can generate a pulse train with seamless frequency by using this methodology. After 
modifying the

 

ND_COUNT_1

 

and 

ND_COUNT_2

 

you should call 

GPCTR_Control

 with 

action = 

ND_SWITCH_CYCLE

 

to activate the new duty cycle.

ND_AUTOINCREMENT_COUNT

The value specified by 

ND_COUNT_1

 is incremented by the value selected by 

ND_AUTOINCREMENT_COUNT

 every time the counter is reloaded with the value specified 

by

ND_COUNT_1

. 

For example, with this feature you can generate retriggerable delayed pulses with 
incrementally increasing delays. You can then use these pulses for applications such as 
equivalent time sampling (ETS). Corresponding legal values for paramValue are 0 
through 2

8

 – 1. 

ND_UP_DOWN

When the application is 

ND_SIMPLE_EVENT_CNT

 or 

ND_BUFFERED_EVENT_CNT

, you can 

use the up or down control options of the DAQ-STC general-purpose counters. You can use 
the up or down control options for other counter applications, too. Software or hardware can 
perform the up or down control.

Table 2-27.  Legal Values for paramValue when paramID = 

ND_INITIAL_COUNT

0 through 2

24 

– 1

0 through 2

32 

– 1

Table 2-28.  Legal Values for paramValue when paramID = 

ND_COUNT_1

, 

ND_COUNT_2

, 

ND_COUNT_3

, and 

ND_COUNT_4

0 through 2

24

 – 1

0 through 2

32

 – 1