NI 9401 counter/digital input/output

[Trainee123]

Hello,

I am a beginner in national instrument product and labview. I bought a NI 9401 and a cDAQ 9174 chassis for my project. Sorry to ask this question but I am really confused about the counter and digital usage of NI 9401. It has 8 channel DIO 0 to 7. Does that means it has 8 counters as well? Can I wire 8 5V TTL signals into all the input terminal DIO 0 to 7?

I am looking forward to the replies. 

[thoult]

You can wire 5 V TTL signals into all of the terminals, but in order to clock any of them against the timebase as a counter you will be limited by the fact you're using cDAQ rather than cRIO.

From memory you only ever used to be able to create two counters for a 9401 in a cDAQ chassis, but I believe the newer ones (like yours) should allow you to configure up to four, depending on how you're trying to use them.

[Trainee123]

Thank you very much!

I have another question. I wanted to mesure the frequency of a 5V TTL pulse signal with a constant fix sample rate. To do that, I tried CI Freq for a DAQmx Create Channel followed by a DAQmx Timing.  I was able to get the frequency value from a DAQmx Read in a while loop by configuring "Implicit" on the DAQmx Timing function. But the sample rate is not constant. I then switched to "sample clock" on the DAQmx Timing function.

My question is which external sample clock source should I select? I kept getting error for every sample clock that I tried in the drop down list. 

Please help me.

[Steve_Block]

I'm able to drive DIO lines using the counter, but that cuts my maximum clock rate in half and requires an extra step in the code. Is there a way to directly route the Counter output through a DIO pin?