How do I handle a two speed spindle?

I have a two speed spindle on my Hurco,

I need a command from the controller to switch to low speed, then my spindle drive sends a signal back to the controller when its in low.

I would need it to be

if M3<3500 enable low speed which would make the output high to close the low speed contactor, then when input is true it can run in low.

Would this be part of a M code subroutine?

I have searched through the hal manual and main manual trying to find a piece on this and had no luck.

Thanks!

Jake