The pulses applied to input C of the SAA1027 integrated circuit determine the engine speed. Each pulse corresponds to a step forward. Input M (mode) determines the direction of rotation of the motor while input R (reset) serves to take the motor to its initial position. The circuit can excite 4-phase stepper motors with currents up to 500 mA. For a supply voltage of 12 V Rx it must be 130 ohms.
