excites the stepper motor using half-step sequence but the excitation method can
be changed to any sequence you choose simply by modifying the startstep
lookup-table with the appropriate sequence of excite output.
single stepped by setting the step_con.0 bit or run continuously by setting the
step_con.1 bit. Modifying the step_lo and step_hi registers sets the rotation rate.
To calculate the values of step_lo and step_hi for a desired revolution rate the
following equation can be used:
steps = number of steps/rotation for stepper used