BLtouch has 5 pins. Why does this board have 4 ports?

[july7d]

BLtouch has 5 pins. Why does this board have 4 ports?

[AnHardt]

Two of the BL-Touch pins are ground (GND).

[GhostlyCrowd]

If you're not running a buck converter to say power the BL touch then only one ground is needed. If you are then you want the red and brown to go to the buck converter and the black ground goes to the board so the logic doesn't have a floating ground from the board when the servo (yellow) and trigger (white) pins are signalling.

That's why the BLtouch has 2 grounds, and since the board is fully capable of powering it, it only needs one because it does not create a floating ground situation.