Differential signals

MASSO is one of the few CNC controllers that provide differential Axis output signals to the motors but what is a differential output and why are they so good?

Until I started working for MASSO I had never seen a controller use differential signals for the axis output. All controllers I had come in contact with used common ground signals which I should mention MASSO also outputs on the axis, so MASSO is compatible with older hardware as well.

Common ground outputs require the use of shielded cable between the controller and the motor drive with the shield connected to Earth at one end of the cable to shield it from noise.
Differential outputs use twisted pairs and do not require shielded cable between the controller and the driver. This is especially good for integrated motors such as the MASSO Closed loop stepper motor which has the motor and drive all in one package and is one of the few stepper motors that use differential signalling

What is a Differential signal
In the diagram below the Original signal is fed into a differential transmitter which converts it into 2 different signals. The first is a copy of the original while the 2nd is an inverted copy of the original signal. These are then sent over a pair of twisted wires to the receiver at the remote end.

If during the transmission, any noise that is introduced to the signal (shown in Red) will be induced evenly into both wires as shown above. These signals then enter the Differential receiver at the motor driver.
Inside the Differential receiver the inverted and non inverted signal enters the differential amplifier where one of the 2 signals is inverted while the other remains unchanged.

The Yellow and blue signals add together as shown below. Note that the noise, shown in red, cancels each other out, as they are exact opposites of one another to give the final result shown in green.

THE POSITIVE & NEGATIVE RED PEAKS CANCEL EACH OTHER OUT TO
GIVE THE ORIGINAL PULSE

How do I know if my Drives are Differential
The first thing to check is the drives manual which will tell you if it is a differential drive.
Differential drives use 4 wires, 2 for the step and 2 for the direction. If your drive uses only 3 wires then it is a common ground drive and not differential. If your drive uses 4 wires but it has optocouplers which seem to be the most common type of drive then it is not a differential drive and just like the common ground drive you must use shielded cable between MASSO and the drive.
MASSO will work with all 3 types of drive inputs so no matter what type you have, you are covered.