Timed loop source: DAQmx create timing source

[Baran_]

I want to use a timed while loop with 120 Hz timing source.

I used "DAQmx create timing source" for generating 120 Hz clock.

What is the input "counter" of this block? And how should I set it?

[Alexander_Sobolev]

Counter is a chip on a physical board, that actually generates the timing pulses.

Create a constant, it will show available counters if any

You can also create software 1 kHz timing source using a "Create timing source" function from Timed structures palette. I can not imagine why you would need hardware triggered timed source not on real-time system.