External reference for USB 5132

Question

Hello,
I have a couple (hopefully) general questions about using an external reference clock on our USB 5132 digitizer.  We want to lock it to the other oscillators in our system, all of which are presently locked to one 10 MHz reference.  If I connect our existing 10 MHz reference to the PFI1 input, my questions are:
1.  Is the 5132 now locked to our system?  Or, do we need to specifiy in the setup software that we want to override the 5132's internal reference and rely entirely our external reference?
2.  In order to have the best possible lock, do we need to tell the 5132 to sample at a frequency that is evenly divisible by 10 MHz (e.g. 20 MHz, 10 MHz, 5 MHz, 2 MHz, etc.)?  Similarly, are we worse off if we want to sample at say, 13 MHz?
Thanks for any thoughts.
Best regards,
Penny
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Answer 1

Hello Penny,
1. Yes the 5132 is locked to your reference system 10MHz clock (with some offset due to delay in the time it takes to transmit the clock signal from your system to this USB device) if you selected the PFI line as the source of an external timebase. Please take a look at the following example Help>>Find Examples>>Hardware Input and Output>> Modular Instruments>>NI-Scope>>Features>> niScope EX External Clocking.vi.
2. No, although I would expect that if you enter in 13MHz and your device was not capable of doing this it would coerce it to the closest value. I would suspect that only integer divide downs from the clock in question are valid such that 12. 5MHz is the value it would coerce to if you were to request a 13MHz value (with a 50MHzexternal clock). The 5132 can not do RIS so sampling at 20MHz with a 10MHz SampleClock Timebase Source is not feasable. 
Regards,
Izzy O.
Applications Engineer
National Instruments
www.ni.com/support