Generate a variable pulse train frequency or clock

I've been trying to raise this on the PXI board (https://forums.ni.com/t5/PXI/Generating-a-variable-clock-pulse-train/td-p/3959809) but realise this may have been the wrong place.

I have a PXI 6683H card, and am trying to generate a variable clock - that is, I want to generate some kind of clock, but then vary the clock frequency without completely killing the clock and starting again.  I've tried some hacked up version of Generate Digital Pulses.vi from the example, but that tops out around 40Hz, and I was hoping to vary between 0 and 1MHz or so.

I might be able to specify the different clock rates in advance, if that helps.