Unipolar stepper motors only require current to flow in a single direction, which makes hardware design simpler because only a low side switch/driver is required (a switch to conduct current to ground from the component - see Figure 1). The high-side of the motor phase is connected directly to the supply voltage without a switch. Unipolar stepper motors can be driven by a stepper motor sequence using a peripheral driver - ULN2003A and TPL7407L are examples of devices that can drive these stepper motors. See Section 3.1 for additional information regarding how to connect a stepper motor to a peripheral driver.
Unipolar stepper motors come in three primary wiring configurations, 5-wire, 6-wire, and 8-wire, where 5-wire and 6-wire stepper motors are the most common. In a 5-wire stepper motor the center tap connections are shorted together internally as shown in Figure 2. In a 6-wire stepper motor the center tap connections are separate connections as shown in Figure 3. A 6-wire stepper motor can effectively act as a 5-wire stepper motor by connecting the two center tap wires.