User manual

Chapter 3 Software Overview

inactive, the counter value latches to the Hold Register. You then can call

CTR_EvRead

to retrieve the saved value. Pulse width is then equal to the

value returned by

CTR_EvRead

timebase. When the counter value is

latched to the Hold Register, the counter reloads itself with a zero and

waits for the gate to go active to begin a new measurement.

For measuring pulse width, you need a rough estimate of the duration of

the pulse being measured. When you configure a counter to measure pulse

width, the counter continues counting in case of overflow. No counter value

is latched to the Hold Register until the gate signal becomes inactive.

To detect the counter overflow, feed the output of the pulse-width

measurement counter to the source input of an event-counting counter.

If the event-counting counter value is not zero after the pulse-width

measurement, the pulse-width measurement is not correct.

Interval Counter/Timer Functions

The Interval Counter/Timer functions perform interval timing I/O and

counter operations on the 516 devices, DAQCard-500/700, Lab and

1200 devices, and LPM devices.

Refer to the NI-DAQ Function Reference Online Help file to determine

which functions your device supports.

ICTR_Read

Returns the current contents of the selected counter

without disturbing the counting process and returns

the count.

ICTR_Reset

Sets the output of the selected counter to the

specified state.

ICTR_Setup

Configures the assigned counter to operate in the

specified mode.