Stepper motors come with a variety

Stepper motors come with a variety of winding and rotor combinations. In addition, there are different ways to sequence energy to the field coils. All these factors deter- mine the size of each step. Phase refers to the number of separate winding circuits. There are two-, three-, and four-phase steppers, which are discussed next.
Two-Phase (Bipolar) Stepper Motors The two-phase (bipolar) stepper motor has only two circuits but actually consists of four field poles. Figure 8.8(a) shows the motor symbol, and Figure 8.8(b) shows how it is wired internally. In Figure 8.8(b), circuit AB consists of two opposing poles such that when voltage is applied (+A –B), the top pole will present a north end to the rotor and the bottom pole will present a south end. The rotor would tend to align itself vertically (position 1) with its south pole up (because, of course, opposite magnetic poles attract).