If you have a multifunction DAQ device, then you could use a counter on the device to generate a TTL pulse signal. Counters can be used to generate a single pulse or continuous pulse trains.
I would suggest to look at example programs to find out how to program with counters. In LabVIEW, there are a variety of example programs that interface with counters. If you're using a text-based programming language, there are examples installed with NI-DAQ that can be found within the ...\Program Files\National Instruments\NI-DAQ\Examples directory.
I hope this helps.
Regards,
Todd D.
