Also try NJR who have taken over Ericsons stepper drivers. they have a good set of data sheets app notes and driver info . This topic is very complex and really an analogue electronics issue if you wish to progress beond basic "make it turn". I have had a fair ammount of experience here and frankly for an area that is as universaly applicable I feel that the driver support technology needs attention from the manufacturures of these devices . Allegro has probably the most versatile approach in there A3977 series , but the pinout seems atrocious to me as you have power pins on both sides off signal pins. Hope this helps Terry