EMC Spindle control Help!

Hello Group,

How does EMC send Cutter spindle speed to the controllers?
I.e. stepper = step/dir = 2 Pins from printer port.

I have a variable motor controller board that is controlled by
voltage.
The input has 3 wires lets say A B C.

Voltmeter Testing.

A and C = 12V Steady
A and B = Variable voltage 2.3 - 9.7 V Approx.
B and C = Variable Voltage 2.3 - 9.7V Approx.

When A + B carry low Volts, B + C are carrying high Volts and vice
versa (I.E. they complement each other and are relative adding up to
the total of 12V)

The Higher voltage across B and C = Faster Motor Speed
The Higher voltage across A and B = Slower Motor Speed

So when B and C are reading max voltage the voltage to the motor is
approx. 190V.

BTW this is off of a very old CNC machine.

What I am going to need to-do is have these voltages controlled via
EMC + a circuit to produce the above output voltages.

Does anyone have any idea what is required or what this circuit is
called.

Congratulations on getting this far ... ;-)

TIA
Steve.