User manual

Chapter 3 Software Overview
NI-DAQ User Manual for PC Compatibles 3-92 ni.com
Interval Counter/Timer Operation for the
ICTR Functions
Figure 3-35 shows the 16-bit counters available on the 516 devices,
DAQCard-500/700, Lab and 1200 devices, and LPM devices.
Figure 3-35. Interval Counter Block Diagram
Each counter has a CLK input, a GATE input, and an OUT output signal.
Use a counter to count the falling edges of the signal applied to the
CLK input. The counter GATE input gates counting operations. If your
device uses an 8253 or MSM82C54 chip, refer to the data sheet in your
device-specific manual to see how the GATE inputs affect the counting
operation in different counting modes.
Interval Counter/Timer Application Tips
NI-DAQ interval counter functions interface to the six different counting
modes of 8253 counter chips on these devices. To choose the mode of
operation, call
ICTR_Setup
. Refer to the
ICTR_Setup
function
description in the NI-DAQ Function Reference Online Help file for
descriptions of all six different counter modes.
After a counter is armed with
ICTR_Setup
, call
ICTR_Read
to retrieve
the current counter value. Furthermore, to halt any counter operation,
call
ICTR_Reset
.
GATE
CLK
Counter OUT