This H-bridge allows 4 states for each half [high (1,0) / low (0,1) / high impedence (0,0) / (1,1) illegal state] by controlling the input signal we determine the direction of current in the motor (coil).
Using three not gates, direction control can be achieved using a single input.
Zener diode is for protection when the supply is suddenly taken out during operation .. As the four diodes will not have a path to discharge the coil
Ultra low input current because of the darlington configuration.
Also those half h-bridges can be used to interface any othe type of motors using proper controlling signal
