National Instruments Welding System 321645c-01 Manual De Usuario

Chapter 2

Function Reference — GPCTR_Set_Application

NI-DAQ FRM for PC Compatibles

2-218

©

 National Instruments Corporation

The following pseudo-code continuation of the example given earlier illustrates what 
you can do to read the counter value continuously (

GPCTR_Watch

 function with 

entityID =

ND_COUNT

 does this) and print it:

Repeat Forever

{

GPCTR_Watch(deviceNumber, gpctrNum, ND_COUNT, counterValue)

Output counterValue.

}

When the counter reaches terminal count (TC), it rolls over and keeps counting. To check if 
this occurred, use 

GPCTR_Watch

 function with entityID set to 

ND_TC_REACHED

. Refer to 

Table 2-32 for TC for E Series, 445X, 455X, and 6602 devices.

 

Typically, you will find modifying the following parameters through the 

GPCTR_Change_Parameter

 function useful when the counter application is 

ND_SIMPLE_EVENT_CNT

. You can change the following:

•

ND_SOURCE

 to any value

•

ND_SOURCE_POLARITY

 to 

ND_HIGH_TO_LOW

•

ND_INPUT_CONDITIONING

 (6602 and 455X devices only) to any value.

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

. 

ND_SINGLE_PERIOD_MSR

In this application, the counter is used for a single measurement of the time interval between 
two transitions of the same polarity of the gate signal. By default, the events are low-to-high 
transitions on the default gate connector pins (see Table 2-25). The counter counts the 20 MHz 
internal timebase (

ND_INTERNAL_20_MHZ

), so the resolution of measurement is 50 ns. The 

counter counts up starting from 0.

With the default 20 MHz timebase, combined with the counter width (24 bits), you can 
measure a time interval between 100 ns and 0.8 s long. For the 6602 devices with counter 
width 32 bits, you can measure a time interval between 100 ns and 214 s long.

Table 2-32.  Terminal Count

2

24

 – 1

2

32

 – 1