arm start trigger with ni9401

[Trainee123]

Hello,

I am using NI 9401 and cDAQ 9174 to count edges from a 5V TTL signal. I wired the TTL signal to pin 16. I wanted to trigger the count using arm start trigger. So I generated a digital pulse from "cDAQ3Mod3/port0/line7" and route it to "/cDAQ3Mod3/PFI0". But all I got was an error like this:

How should the arm start trigger be used in this case? What are the routing necessary? Can somebody help me please?