alternating inputs using timed loop

Hi,

I am trying to supply alternating inputs to an instrument using Labview 2011.

I need to supply a value of 1 volt for 10 ms, then a value of 2 volts for 10 ms (then 1 volt and then 2 volts again) and the pattern should repeat continously.

How do I implement this alternating sequence in Labview using a time delay or timed loop?

I need to avoid using a square waveform because the instrument does not recognize it.

Hardware timing would be preferable because it needs to be precise.

Thanks.