National Instruments NI 6238 - Manual (Page 126)

Chapter 10 Digital Routing and Clock Generation
NI 6238/6239 User Manual 10-10 ni.com
When a PFI input is routed directly to RTSI, or a RTSI input is routed
directly to PFI, the M Series device does not use the filtered version of the
input signal.
Refer to the KnowledgeBase document, Digital Filtering with M Series
and CompactDAQ, for more information about digital filters and counters.
To access this KnowledgeBase, go to
ni.com/info and enter the info
code rddfms .