Driver & Receiver
The Enable signal of the driver allow for multiple drivers on the bus. Only one driver’s Enable signal should be ON during a transmissions, while the others are OFF, “disconnecting” these driver from the bus (this third output state is called tristate). If more then one Enable signal is ON, output voltages could come into conflict.
Often the Enable line of the receiver is hardwired so that it signals the opposite state of the Enable signal of the driver on the same node. So the node will not receive an echo of it’s own transmission.
The signal is transmitted using a balanced differential system, where the logical state is determined by the voltage difference UD/R of the signal lines: UD/R = UB - UA