I'll be not so sure that every CNC uses step motors. All real CNC machines I've seen use servos.
Could you please tell us what is your application?
What kind of CNC do you have?
OK, i have mach3 software... and now i want to convert the output of mach3 (for steper motors) to servo motors. Do you have any idea how can i do that?.
I think that the easiest way to do what you want is to get a servo driver with pulse and direction input.
I remember having worked with some servo driver from Allen Bradley that have analog voltage input and pulse direction input, but I can't remember now the part number.