National Instruments NI 5911 User Manual

Also see for NI 5911: Getting started guide

Contents

National Instruments NI 5911 User Manual Manual pdf 23 page image

Chapter 2 Hardware OverviewNI 5911 User Manual 2-12 ni.comPFI Lines as InputsYou can select PFI1 or PFI2 as inputs for a trigger or a reference clock.Please see the Synchronization section below for more information aboutthe use of reference clocks in the NI 5911.PFI Lines as OutputsYou can select PFI1 or PFI2 to output several digital signals.Reference Clock is a 10 MHz clock that is synchronous to the 100 MHzsample clock on the NI 5911. You can use the reference clock tosynchronize to another NI 5911 configured as a slave device or to otherequipment that can accept a 10 MHz reference.Frequency Output is a 1 kHz digital pulse train signal with a 50% dutycycle. The most common application of Frequency Output for the NI 5911is to provide a signal for compensating a passive probe.SynchronizationThe NI 5911 uses a digital phase locked loop to synchronize the 100 MHzsample clock to a 10 MHz reference. This reference frequency can besupplied by an internal crystal oscillator or through an external frequencyinput through the RTSI bus clock line or a PFI input.The NI 5911 may also output its 10 MHz reference on the RTSI bus clockline or a PFI line so that other NI 5911s or other equipment can besynchronized to the same reference.While the reference clock input is sufficient to synchronize the 100 MHzsample clocks, it is also necessary to synchronize clock dividers on eachNI 5911 so that internal clock divisors are synchronized on each differentdevice. These lower frequencies are important because they are used todetermine trigger times and sample position.To synchronize the NI 5911 clock dividers, you must connect the digitizerswith an NI RTSI bus cable. One of the RTSI bus triggers must bedesignated as a synchronization line. This line will be an output from themaster device and an input on the slave device. To synchronize thedigitizers, a single pulse is sent from the master NI 5911 to the slaves. Thispulse supplies the slave devices with a reference time to clear their clockdividers. Hardware arming cannot be used during an acquisition usingmultiple devices. For more information about synchronization, refer toyour NI-SCOPE Software User Manual.