For X Series and NI 661x devices, you can filter digital I/O lines and input signals.

You can configure digital filters on the device by choosing three fixed values (90 nS, 5.12 µS, 2.56 mS). For each digital line or input terminal, there are four attributes/properties associated with these digital filters: Digital Filter Enable, Digital Filter Minimum Pulse Width, Digital Filter Timebase Source, and Digital Filter Timebase Rate.

When you set the Digital Filter Enable to true, you must also configure the Digital Filter Minimum Pulse Width attribute/property. This value represents the minimum value that is guaranteed to be passed into the device. The maximum pulse guaranteed to be blocked by the device varies by digital line. Refer to your device documentation for details. When you select a custom filter value with the Minimum Pulse Width attribute/property, NI-DAQmx uses an internal 32-bit utility counter to generate the desired filter value. If you would like to generate the filter clock using your own external signal, you can use the Digital Filter Timebase Source and Digital Filter Timebase Rate attributes/properties. You must configure both to use an external signal as the source for the digital filter.

When using digital filtering on port 0, you can enable bus mode using the Enable Bus Mode attribute/property. When enabled, the device observes changes to multiple lines as a single change if these conditions are met:

• The skew between them is less than the minimum pulse width of the filter.
• The lines remain stable for an additional minimum pulse width of the filter.

When using any other signal on the device that supports filtering (excluding port 0), you can select a custom filter value in addition to the three fixed values mentioned previously. The custom filter value must be the same for all lines across the device. For example, if you choose a filter value of 2 µS for PFI 0, any other filterable line on the device can only choose from the three fixed values and the 2 µs value selected for the custom filter.

The following table lists the attributes/properties for terminals that can be digitally filtered.