Reuse Makerbot SMD-2.3 Stepper Driver with Arduino
From http://reprap.org/wiki/Stepper_Motor_Driver_2.3#IDC_Connector

IDC Connector

Pin     Name    Function


N/C     Not Connected to anything
GND     Connect this to your uC to share a common ground.
Step    A pulse on this line will make the stepper motor advance one step in the desired direction.
Dir     If this pin is high, the motor will rotate forward, low it will rotate backwards.
!Enable    This pin allows you to turn the motor on and off. It is an inverted pin to avoid noise turning the driver on. By default it is disabled (pulled high). A high signal means off, low signal means on.
Min     This is the signal from the 'min' sensor. The definitions of high/low are determined by your opto endstop.
Max     This is the signal from the 'max' sensor. The definitions of high/low are determined by your opto endstop.
GND     Connect this to uC to share a common ground.
GND     Connect this to uC to share a common ground.
GND     Connect this to uC to share a common ground.