OUT1A is one of the output pins of the A4988 Stepper Motor Driver IC. This pin, along with OUT1B, serves to control one winding of a bipolar stepper motor.

When the IC is enabled and depending on the direction (DIR) and step signals (STEP), current is sent through OUT1A and OUT1B in a specific sequence. This generates a magnetic field in the coils of the motor and causes the shaft to rotate step by step.

Bear in mind, the output pins connect to the coils of the stepper motor and the polarity of the voltage applied to these pins defines the direction of the current flow through the winding, which in turn determines the direction of the magnetic field and thus, the direction of stepping.

Remember to connect the stepper motor to these outputs observing the correct polarity and coil pairings.