Hello Amit.
There are a few great example programs in NI Example Finder that show how to do digital reads and writes with an external clock. Read Dig Port - Ext Clk and Write Dig Chan - Ext Clk are both examples that can be found in the NI Example Finder. Also, in these same directories (Hardware Input and Output>>DAQmx>>Digital Generation or Digital Measurements) are numerous other examples that will get you familiar with using an external clock to acquire digital signals. The 6259 is compatible with the VI's specifically mentioned.
In terms of measuring voltages and currents, you can directly connect the signals as long as they fall in the current and voltage range of the card. Depending on the amplitude of the voltage and current, and how noisy your environment is, some filtering or amplification of the signal could be necessary to retrieve a good signal. However, it still always helpful in improving the quality of the signal.
Let me know if you have any other questions.
Have a great day!
Brian F
Applications Engineer
National Instrumetns
