The 3 Hall Effect Sensors enable the switching circuit to "know" exactly where the rotor is positioned in relation to the motor's 6 steps. In the example above, the Hall Sensor near coil "C" detects that it is in the vicinity of a South Pole magnet and sends a signal to the decoder to turn on coil "C" to South Polarity. The Hall Sensor near coil "A" detects that it is in the vicinity of a North Pole magnet and sends a signal to the decoder to turn on coil "A" to North Polarity. The Hall Sensor near coil "B" detects a gap with no magnetic field, and sends a signal to ensure that coil "B" is turned off for that step. "AN CS" means "A North C South". "AH CL" is the same, but refers to 2 transistors, a High Side MOSFET "AH"which switches the positive supply to the motor, and a Low Side MOSFET "CL" which switches the motor to ground or negative. There are 6 MOSFETS, and they switch in the following sequence.
BL AH, AH CL, CL BH, BH AL, AL CH, CH BL
One MOSFET is not switched off each step to make the required transition.