Almost all of NI's digital DAQ products support only 5 V TTL logic, as this is the most prevalent. If you need to read 3.3 V signals as an input, you may generally directly connect the signals to the DAQ board because 5 V TTL considers anything above 2.2 V to be a logical high. However, if you are outputting signals to a device that requires 3.3 V signals, you will need to reduce the voltage. The best way to do this is to use a bus transceiver with voltage shifting, such as these:
These can also be used for voltage shifting on input, should it be necessary.