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change detection on port 1 of PCI-6221

Hi Experts,

I am having a little trouble using dynamic events with port 1 of my PCI-6221 DAQ card (37 pin D-sub connector variant).

Attached is a simple test VI. Three digital input lines are configured to provide a change detection event which is read in the event structure.

There is no problem using either of the port 0 lines (the 37-pin 6221 has only two port 0 lines), the events are being responded to in the event structure. However, the port 1 digital input line does not seem to respond to the events.

No error messages are generated, and I know the DAQ card is working ok as all three lines are being correctly read when the event for either port 0 input fires.

So basically, is there some magic configuration involved in getting port 0 and port 1 to both respond to change detection events? I cannot find any substantial documentation for the change detection event anywhere

Any ideas?

Many thanks
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Message 1 of 4

Sorry for the delay, you have had me puzzled with what was going on here, although I know have got to the bottom of this. The answer is actually quite simple and is down to the hardware architecture of our M-Series boards. In your case you have 3 digital ports, but although they seem it, they are not all the same. With all multifunction DAQ boards, only Port 0 is what we call correlated. Correlated I/O enables synchronization of onboard digital I/O lines to a clock reference. All the other ports are just static DIO. This is the reason that you can only perform change detection on digital lines from port 0. Have a look  at the change detection section of the KnowledgeBase What Options Do I Have for Hardware-Timed Digital I/O on my M Series DAQ Device.

So basically you need to change the final line you are monitoring from port1/line7 to another line on port0.

I hope this helps.


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Hi nrp,

In addition to what Rich said, adding lines from port1 or port2 to the rising edge physical channels or falling edge physical channels inputs of DAQmx Timing (Change Detection).vi should have generated an error, indicating that this is not supported. The lack of error in this situation has been reported to R&D as CAR #108075.

Brad Keryan
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Message 3 of 4
Thanks for your insight.

Unfortunately, I bought the 37-pin flavour of the PCI-6221, and this only has two port 0 pins (as well a full width port 1). This is really a pity as I could have done with the buffered input, and now I have to resort to polling.
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