© National Instruments | 5-31NI cDAQ-9181/9184/9188/9191 User ManualFigure 5-34 shows a block diagram of the frequency generator.Figure 5-34. Frequency Generator Block DiagramThe frequency generator generates the Frequency Output signal. The Frequency Output signalis the Frequency Output Timebase divided by a number you select from 1 to 16. The FrequencyOutput Timebase can be either the 20 MHz Timebase, the 20 MHz Timebase divided by 2, orthe 100 kHz Timebase.The duty cycle of Frequency Output is 50% if the divider is either 1 or an even number. For anodd divider, suppose the divider is set to D. In this case, Frequency Output is low for (D + 1)/2cycles and high for (D - 1)/2 cycles of the Frequency Output Timebase.Figure 5-35 shows the output waveform of the frequency generator when the divider is set to 5.Figure 5-35. Frequency Generator Output WaveformFrequency Output can be routed out to any PFI terminal. All PFI terminals are set tohigh-impedance at startup. The FREQ OUT signal also can be routed to many internal timingsignals.In software, program the frequency generator as you would program one of the counters forpulse train generation.For information about connecting counter signals, refer to the Default Counter/Timer Routingsection.Frequency DivisionThe counters can generate a signal with a frequency that is a fraction of an input signal. Thisfunction is equivalent to continuous pulse train generation. Refer to the Continuous Pulse TrainGeneration section for detailed information.For information about connecting counter signals, refer to the Default Counter/Timer Routingsection.100 kHz Timebase20 MHz TimebaseFrequencyOutputTimebaseFREQ OUTDivisor(1–16)Frequency Generator÷ 2FrequencyOutputTimebaseFREQ OUT(Divisor = 5)
