The SilentStepStick Protector is an addon module for StepStick and Pololu A4988 compatible stepper motor drivers. The board provides flyback diodes (freewheeling diodes) for the motor outputs, so that they are also protected against induction voltages in the unpowered state of the driver.
The protector also contains a diode from the logic voltage (anode) to the motor voltage (cathode), so that the power supply order of all SilentStepSticks is always guaranteed.