yep, that what i was hoping for,
use the 57cnc board to run the machine, motors, spindle, encodes, mdi's etc then use a 57U board for the buttons (keyboard emulator) and some macros.
I have been trying to do this with a tool changer. on Mach i have put in 8 more buttons 1,2,3 etc to one of the screens for the tool changer. you click on the button and the tool changes. but when i have tried to do this using the 57cnc it works a few times then it goes all funny. as in, it will go through the motions of the tool change two or three times. after a while mach will slow down then stop.
the button is done by the a quick key. pressing "1" will run "code t0101" pressing "2" code t0202 etc. the 57cnc board is set input pin16 "press the 1 key". dont know if this is right or wrong, but as i said it works a few times, then goes funny.