Checking when an output becomes available

Question

I typically use error out / error in signals to sequence the execution of my VIs. However, I am using a really old instrument with an old VI (HP 54501A oscilloscope if you are interested). Basically, my task is that I want to trigger the oscilloscope through hardware (BNC cable) and only then acquire data from the oscillloscope.
The triggering instrument is an Agilent 33250A function generator (have to use a VISA write to switch its output trigger on). However, how do I correctly sequence the oscilloscope read VI in the code - it must occur immediately after (the excitation is about 200 microseconds long) the output on the agilent is switched on ?
There is no error in input to the HP VI. I have thought of writing a dummy or gate that provides one of the inputs to the HP VI (after a calculation) but since the OS is non-deterministic (Linux), there is no way of ensuring that the oscilloscope read will take place at the right time. 
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Answer 1

Thanks for the response, and the question.
The issue here is that the fngen puts out a two period burst of a custom waveform. I want to monitor the response as a function of time during that burst.
With the software trigger, I do not know (I could be wrong on this), whether the process of excitation and measurement are going to be sync'ed. That is why I want to use a TTL signal from the fngen to trigger the scope on an unused channel (channel 2), do a single sweep and get the waveform.
For sanity check purposes, I am using channel 4 on the scope to monitor the burst and channel 1 for the response. That way, I hope to get both the signals on the same time scale and see if there is a triggering delay imposed by the coax BNC connecting the fngen to the scope.
A later post has really cleared up one of the cobwebs in my mind (as I think of it) - I just need to check if it was triggered *after* the measurement is complete and get the waveform.
And a big thanks to whoever suggested that I search for the manual on Agilent's website. Here is a link:
http://www.home.agilent.com/agilent/techSupport.js​px?pid=322798&pageMode=MN&cc=US&lc=eng
Duh
I will keep you guys posted to see if this works.