National Instruments 6711 User Manual

Also see for DAQCard-6715: User manual User manual

Contents

National Instruments 6711 User Manual Manual pdf 52 page image

5-8 | ni.comChapter 5 CountersMaster Timebase SignalThe Master Timebase (MasterTimebase) signal, or Onboard Clock, is the timebase from whichall other internally generated clocks and timebases on the board are derived. It controls thetiming for the analog output and counter subsystems. It is available as on output on the I/Oconnector, but you must use one or more counters to do so.The maximum allowed frequency for the MasterTimebase is 20 MHz, with a minimum pulsewidth of 23 ns high or low. There is no minimum frequency limitation.The two possible sources for the MasterTimebase signal are the internal 20MHzTimebase signalor an external signal through RTSI 7. Typically the 20MHzTimebase signal is used as theMasterTimebase unless you wish to synchronize multiple devices, in which case, you should useRTSI 7. Refer to Chapter 8, Real-Time System Integration Bus (RTSI), for more information onwhich signals are available through RTSI.Figure 5-10 shows the timing requirements for MasterTimebase.Figure 5-10. MasterTimebase Timing RequirementsGetting Started with Counter Applications inSoftwareYou can use the AO Series device in the following counter-based applications.• Counting Edges• Frequency Measurement• Period Measurement• Pulse Width Measurement• Semi-Period Measurement• Pulse GenerationYou can perform these measurements through programmed I/O, interrupt, or DMA data transfermechanisms. The measurements can be finite or continuous in duration. Some of theapplications also use start triggers and pause triggers.Note For more information about programming counter applications and triggersin software, refer to the NI-DAQmx Help.tp = 50 ns minimumtw = 23 ns minimumtw twtp