The IN1, IN2, IN3 and IN4 pins can be connected to any digital or analog input pin on the board.
The PUL- (PUL) and DIR- (DIR) pins can be connected to any digital or analog input pin on the board.
Connecting ENA-(EN) is optional and only required when the stepper should be enabled by a specific simulator output (for example, auto-throttle or autopilot engaged).
