In this blog post (https://industruino.com/blog/our-news-1/post/industruino-as-stepper-motor-driver-25) you control a UNIPOLAR stepper motor directly, but you mention that "it is impossible to drive a bipolar stepper motor with high-side drivers only" because the high side drivers cannot sink any current. What would be the best way to control a BIPOLAR motor with the D21G?
The best way would be to use an external stepper motor driver that either takes STEP/DIRECTION control signals (which can come from the IND.I/O's digital output pins) or uses an RS485 port which you issue serial commands. The RS485 type stepper motor driver would probable cost a bit more but it gives you a lot more control and almost unlimitted amount of drivers can controlled from the same bus. Offcourse, all depends on the speed/latency requirements of your application.
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