Stepper motor with driver A4988

batata004:
@saximus Are you sure the number inside delayMicroseconds is related directly to RPM?

Yes, that is how these motors work. You even did the same calculation in your OP.

batata004:
Anyway, with 500 my motor is spinning fine.

Obviously it isn't or you wouldn't be asking questions about why it isn't working how you expect it to.

batata004:
Which number are you using in your motor and how many RPM you get with your delaymicroseonds(X)?

750us delay rotates it at 200RPM as expected.