The BUSY control line is used to indicate the status of the internal state machine. When the BUSY line is held low, it indicatesthat the internal state machine is in idle mode and that the radio is ready to accept a command from the host controller.The BUSY control line is set back to zero once the chip has reached a stable mode and it is ready for a new command.Inherently, the amount of time the BUSY line will stay high depends on the nature of the command. For example, settingthe device into TX mode from the STDBY_RC mode will take much more time than simply changing some radio parametersbecause the internal state machine will maintain the BUSY line high until the radio is effectively transmitting the packet.