Why is PFI6 the default HwDigitalTriggerSource for my National Instruments USB-621x device if PFI<4..7> are strictly digital output lines?

When creating an ANALOGOUTPUT for a National Instruments (NI) USB-621x series data acquisition device:

ai = analogoutput('nidaq','Dev1');

the HwDigitalTriggerSource property of the object is set to PFI6, by default:

>> get(ao,'HwDigitalTriggerSource')

ans =

PFI6

However, the PFI6 line on a USB-621x device is configured only for digital output, not input. I would like to know why the default HwDigitalTriggerSource is set to a digital output line in the first place for this device series.

Answer 1

[MathWorks Support Team]

Since there is no direct way through the NI-DAQmx API to determine whether a PFI port is configured for input or output, it is not possible to maintain a list of valid terminals for the various National Instruments boards supported by the Data Acquisition Toolbox. The PFI6 port was traditionally the terminal used by E series devices for ANALOGOUTPUT hardware triggering, and thus was chosen to be the default.

Please consult your NI board documentation to determine whether PFI6 is a digital pin configured for output only. If so, set the 'HwDigitalTriggerSource' property of your ANALOGOUTPUT object to an appropriate pin that is configured for input.