i am working on installing a SuperPid onto a 611. I have a question about this schematic

It shows the TACH output going straight back to the PC through the Parallel Port. I think I am Missing something here. How does it actually connect back to the PC?

I am using Mach3, ESS, & G540.

I assume that this wire should go to one of the Inputs (PIN1-4) on the G540.

Can someone please help clarify this for me?