Error -200264 When Performing Analog Reference Triggering

Issue Details

I'm trying to do analog reference triggering and am getting the following error:

Error -200264 occurred at DAQmx Start Task.vi
 

Solution

If you need pre-trigger samples on multiple channels you cannot use one of the AI channels as the reference trigger source.  You must use PFI0 (E series only) or APFI0/APFI1 (M and X Series only) as the trigger source instead. These are separate inputs that will be continually monitored through an analog comparison circuit. 

Keep in mind you could wire the same signal to both PFI0 (or APF0/APFI1) and your analog input channel.  Doing this would allow you to use one of your signals for your trigger source (through the PFI line) while still acquiring pre-trigger samples for it and the other channels (through AI <0..X>).  For more information about setting up analog reference triggers refer to your device's respective user manual.

Explanation of why this error occurs:

Having more than one channel is the task is not allowed because it is impossible to acquire pre-trigger samples on more than one channel when using a multiplexing card (any card that only has one Analog to Digital Converter and several analog inputs).

The reason it is impossible to acquire pre-trigger samples on more than one channel is because the time it takes to multiplex between channels may be long enough that the trigger will not be detected on the first channel. For example, if the trigger value were to come into AI0, the card could still be multiplexing through the other channels and never detect the trigger. Therefore DAQmx does not allow you to have more than one channel in the task.  It does this to ensure it can continually monitor the correct analog input for the trigger.