Power

• VDD - This is the logic voltage input. To power the board, give it the same power as the logic level of your microcontroller - e.g. for a 5V micro like Arduino, use 5V. It can be powered between from 3.3V to 5V.
• + - This is the motor voltage input. Supply 8V to 35VDC for your motor.
• GND / - (terminal block) - common ground for power and logic.

Current Potentiometer

On the right side of the board is the current potentiometer. This potentiometer limits the current output to the motor. When the potentiometer is all the way to the right, you can get up to 2A max. Note that the higher currents will heat up both the motor driver and stepper, so you may need to add heatsinking to the chip.

Terminal Block Bipolar Stepper Motor Connections

• 1A and 1B - The first set of motor control outputs connected to DMOS bridge 1.
• 2A and 2B - The second set of motor control outputs connected to DMOS bridge 2.

Stepper Control Pins

• DIR - This is the direction control pin. You can set this pin high or low to set the spin orientation. Pulling it high turns the motor clockwise. Pulling it low turns it counterclockwise.
• STEP - This is the microstep control pin. Toggle this pin to take one step or microstep at a time. By default, the driver is set to 1/16 microstep mode.

Microstep Selection Pins

There are three pins (MS1, MS2 and MS3) that can be pulled low to change the default 1/16 microstep mode where all three pins are open/high. The table below shows the pin combinations to change to the different modes. For example, if you wanted to use 1/4 microstep mode, you would tie MS1 and MS3 to ground (closed/low) and leave MS2 as-is (open/high).

A4988 Control Pins

• RST - This is the reset pin. Pull this pin low to reset the A4988 to its home state.
• SLP - This is the sleep pin. Pull this pin low to put the breakout into a low power sleep mode. Pull the pin high to disable sleep mode.
• EN - This is the enable pin. Pull this pin high to disable the output to the motors.

LEDs

• Green LED - The green LED is tied to the DIR pin. It is lit when the motor is being driven counterclockwise when the DIR pin is low.
• Red LED - The red LED is tied to the DIR pin. It is lit when the motor is being driven clockwise when the DIR pin is high.
• Yellow LED - The yellow LED is tied to the STEP pin. It is lit when the motor driver is being moved.

ROSC Jumpers

On the back of the board is a set of jumpers that are tied to the ROSC pin. This pin sets the off-time for the internal PWM current control that determines the off time and decay mode for the motors (how quickly the A4988 reduces current being driven to the motor).

By default, with the jumpers open, the ROSC pin is tied to ground with a 20K resistor, setting the off time to approximately 24.2 μs (resistor value divided by 825). The decay mode is automatic mixed (slow and fast), except when driving the motor in full-step mode. Full-step mode uses slow decay.

If you solder the upper jumper closed, the ROSC pin is tied to VDD. This sets the off time internally to 30 μs. The decay mode is automatic mixed (slow and fast), except when driving the motor in full-step mode. Full-step mode uses slow decay.

If you solder the lower jumper closed, the ROSC pin is tied to GND. This sets the off time internally to 30 μs. The decay mode is automatic mixed (slow and fast) for all step modes.