NI 6251 too many physical device names?

[Jonas_Stein]

the USB NI 6251 BNC should have 8 digital I/O ports, named PFI0..PFI7, but the drop down list consists of 16 possible items.

[Dennis_Knutson]

The 6251 has 3 ports or 24 lines. I have no idea how you only see 16. I see all 24. If you want to select ports, lines, or both, you right click on the channel constant and select I/O Filtering.

[Jonas_Stein]

what is the difference between port and line?

[Jonas_Stein]

and is PFI12 the same like USER1 on the terminal?

Where can i find a table with the naming scheme?

[Dennis_Knutson]

 A port is multiple lines - typically 8 lines in a port.

Refer to the manual.