[hellfire39]

Good morning,
finally, after many years, I'm finishing my cnc with MK2/4 baord as controller.
I'm preparing the hardware interface between the board I/O and the 24V sensors.

I'm asking the meaning of the input called CTRL8. Tha manual defines it as "additional switch". Which use I can make of it (if any)?

I wasn't able to find the string "CTRL8" in the SW manual.

[hellfire39]

I will answer by myself. I think the only useful application for CTLR8 input is for firmware update.
This leaves me with only two fixed function inputs (IN1 and IN5), plus e-stop (CTRL1).

Please, let me know if this is the correct answer.

[PlanetCNC]

CTRL8 pin can also be used for spindle synchronization.

[hellfire39]

Thank you for the answer.
Now it makes sense, for me, consider also this input in my input/output board (even if I cannot sync the spindle at the moment).