oooohhhh.... let's think about this...

Do you really mean 1/256th of a single step... or do you mean there are 256 steps in a revolution and you mean 1/256th of a Revolution?

Most (though not all) stepper motors have four coils. We'll call them A, B, C and D. A step is when we rotate the shaft from one set of coils to the next... Let's also say that coil A is our starting sequence (it doesn't have to be, but for our example it is)...

A to B = A is energised, then de-energise A and energise B = 1st step
B to C = B is energised, then de-energise B and energise C = 2nd step
C to D = C is energised, then de-energise C and energise D = 3rd step
D to A = D is energised, then de-energise D and energise A = 4th step
the cycle now repeats from the top.

This is the conventional way a Stepper Motor rotates. Now the number of steps you have per revolution depends on your actual stepper motor. There's dozens and dozens of variants. Steppers are usually specified in a step angle (eg 1.8 Degrees per Step, or 7.5 Degrees per step), usually a figure divisible evenly into 360 (one rotation). So the 1.8 Degree stepper needs 200 steps for a revolution.

You can drive most Steppers in half-steps... like so...
A only is energised = 1st step
A to AB = B is additionally energised (A+B energised) = 1.5 step
B only is energised = 2nd step
B to BC = C is additionally energised (B+C energised) = 2.5th step
C only is energised = 3rd step
C to CD = D is additionally energised (C+D energised) = 3.5th step
D only is energised = 4th step
D to DA = A is additionally energised (D+A energised) = 4.5th step
the cycle repeats from the top

With this 'half-step' arrangement you now double the steps of your stepper making it twice as accurate. So if you had a Stepper that needed 200 steps per revolution (our 1.8 Degree Stepper above), you now can give it 400 half-steps to achieve the same result (which means we've an achieved an accuracy of 0.9 Degrees with our 1.8 Degree Stepper)

Naturally you can reverse the sequence from any point to drive backwards.

Now, can we take that 1.8 Degree step and achieve an accuracy of 1/256th of our 1.8 Degrees? - in other words 0.007 Degree micro-steps?... the answer is No. I've not seen a Stepper with such a complex coil phasing arrangement that it allows 256 micro-steps per individual step. But point me to a Datasheet if you know of one. Trust me, if it exists, we can drive it.