Can I Use Multiple External Clocks With My NI 6552 Device?

[R_Rod]

Can I Use Multiple (External & onboard) Clocks With My NI 6552 Device? I am using a PXI-6552 to generate two different signals.

For the 1st signal, I want to use an external clock input to the 6552 to generate the clock and frequency.

For the 2nd signal, I want to use the 6552 onboard clock to generate the clock and frequency for the 2nd signal.

Any help is appreciated!

[Ryan_M]

R_Rodriguez,

Yes you can use different clocks....but not at the same time.  There's only one generation engine in the device so you can only run your dynamic channels from a single clock source.  That clock can come from many places between tasks, but you may only have one active at a time.  That is, you can run a task from onboard clock and then run a task from the external clock but you can't run one channel with on board and another channel from external at the same time.

I'm not sure of your application requirements, but if the frequencies are related, you could possible use oversamlping to emulate that behavior.  For example, if you want one channel at 10MHz and another at 50MHz, you could use an external 10MHz reference to generate your onboard clock and run at 50MHz.  You would then repeat samples on the 10MHz channel 5 times to get an effective different rate.

[R_Rod]

Can you provide some more detail on how to do this?

[Ryan_M]

There are examples shipped with HSDIO regarding clock selection. 

Regarding oversampling, if you want to generate a 25MHz toggle pattern on a data channel, you can run the clock at 50MHz and generate a waveform with 10101010.  Alternately you can run at 100MHz create a pattern 1100110011001100.  The latter takes up twice as much memory but gives you 10ns of edge placement resolution compared to 20ns if you run at 50MHz.

For oversampling, I would recommend using the Digital Waveform Editor.  If you load a waveform in this tool, you can goto TOOLS >> Resample to expand the waveform.