National Instruments 321645c-01 用户手册

Chapter 2

Function Reference — CTR_Square

NI-DAQ FRM for PC Compatibles

2-112

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 National Instruments Corporation

When you use special gating (gateMode = 8), you can achieve gate-controlled pulse 
generation. When the gate input is high, NI-DAQ uses period1 to generate the pulses. When 
the gate input is low, NI-DAQ uses period2 to generate the pulses. If the output mode is TC 
Toggled, the result is two 50% duty square waves of difference frequencies. If the output 
mode is TC Pulse, the result is two pulse trains of different frequencies.

Figure 2-11.  Square Wave Timing

There is an uncertainty associated with the beginning of square wave generation due to 
counter synchronization. Square wave generation starts on the first timebase edge after 
NI-DAQ applies the starting signal. The time between receipt of the starting signal and the 
start of the square wave generation can be between 0 and 1 units of the timebase in duration.

You should not use edge gating with square wave generation. If you use edge gating, 
the waveform stops after period1 expires and then continues for one total period 
(period2 + period1) only after NI-DAQ applies another edge. For continuous square wave 
generation, use level or no gating.

0 < sync period < 1

1

Timebase

Starting

 Signal

TC Toggle

Output 

TC Pulse

  Output

1

units = timebase period

1

period2

period2-1

period1-1

period1