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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.
IO corresponding figure above

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 )