I/O method, I/O property? CompactRIO question

[jeff_scharpf]

Can someone clarify for me what an "I/O method" is? How do I use this?
I am trying to time incoming pulses on the digital input of a 9421 (CompactRIO). All I want to do is calculate the period of each incoming signal and store it.

I was hoping to use the FPGA to read the digital input, and (if triggered or prompted to start looking) to watch the first digital input (D0) for a signal that will come from an encoder. I need to measure every period and store these values or send them up to the controller to be stored for later processing. The signals will be coming in at a rate of (max 5000 hz) and eventually drop to 0HZ very quickly (within 100 - 200 ms).


I have searched for examples. One says to trigger off of the rising edge. Use the "I/O method" and set it to the rising edge.
I have no idea where to find this property in the "I/O method" node.
I also don't understand what the difference is between this, and just using the digital input node.
Can someone shed some light on this?

Regards,

Jeff

[Danny G.]

Jeff,

The digital input node will read the state of the line when it is triggered, it will not wait until a pulse has come through. Depending on the speed of your read you may be reading the same value multiple times. The method node allows you to wait until a pulse comes into read it.

In order to set up the node in LabVIEW place the method node on the block diagram. The method node is located in the FPGA Device I/O palette. Right click on the method node and select any of the digital lines that have already been configured. Once the line has been selected right click again and all the digital options will be available. One of them is "Wait on Rising Edge".

Regards,

Danny G
National Instruments