Help understanding pins on a stepper motor driver
I remember I had two similar ones in my garage , also without a manual.

I would expect this, but you can measure current with a 220 Ohm R to 5V to verify what the internal R is, if any.

The opto inputs allow you choose polarity of driver from Logic or an open collector comparator.  Arduino outputs can drive this.  

You need step pulse 1~10us min. up to 100KHz? depending on microstep resolution. Direction and Enable.  Out you can check if that is active with a DMM or needs a pullup to Vcc.







simulate this circuit &ndash; Schematic created using CircuitLab

SW4 may be the holding current after step which might be cooler at 50%.

400 Step will give max acceleration, torque and RPM at constant step rate.
Bigger is smoother and quieter but less torque.  You accelerate step rate during seek for max. velocity without cogging/slipping, according to load and adjust current accordingly with average power, holding current,SW4?? with Pd and temp rise of motor. Keep warm not hot.