This expansion board as a driver expansion board, can be used for engraving machines, 3D printers.
It is a total of four slots, can drive four A4988 stepper motor. Each road stepper motors only need two IO ports. In other words, six IO ports can be well managed three stepper motors. Very convenient to use.
UNO for Arduino module IO port correspondence introduction.
UNO for Arduino---------------------- expansion board
8 ------------------------ EN ( stepper motor driver enable , active low )
7 ----------------------- Z.DIR (Z -axis direction control )
6 ----------------------- Y.DIR (Y -axis direction control )
5 ----------------------- X.DIR (X -axis direction control )
4 ---------------------- Z.STEP (Z -axis stepper control )
3 ---------------------- Y.STEP (Y -axis stepper control )
2 ---------------------- X.STEP (X -axis stepper control )

Note: When inserting the A4988 module, must be careful not to insert opposite. Stepper motor wiring as follows:
2A, 2B is a group (red, green), 1A, 1B is a group (blue, yellow), if want to change direction, can be change the position of one group , for example 2A, 2B mutually exchanged.