please solve the whole question step by step.

(a) (i) What distinguishes a communication interface that is a 'bus' from one that is not a bus. Does the UART peripheral (as found on the KL25Z) implement a bus? (ii) Briefly explain the difference between a synchronous and an asynchronous communication interface. (iii) Explain the advantage of a duplex data transmission compared with a half-duplex. (iv) Briefly explain what DMA (direct memory access) is, with an example of how it can be used in the KL.25Z. [8 marks] (b) It may be important to reduce energy used by an embedded system. (i) Explain the way energy is used when the CPU runs. (ii) Describe two techniques available in the KL25Z to reduce energy use while still running the CPU. (iii) A micro-controller, such as the KL25Z, includes a UART for serial communication. Explain how the UART can be used when the CPU is halted (i.e. in wait or sleep mode). [6 marks] (c) A system has the following requirements. An automated pill box is designed to remind a patient to take medication at the right times. The medication should be taken within a time window, such as between 9 and 10 am; there may be several such periods every day. The system waits for one of the periods to start. The patient touches a fingerprint sensor to open the box, provided of course that it is the patient's fingerprint and the correct time. Closing the box returns the system to the waiting mode. If the fingerprint does not match the patient's, an audible signal is produced until the system is reset. Otherwise if the patient is too early (l.e. the next time window has not yet started) the system plays a message "please wait" for 20s. On the other hand, if the time windows ends without the patient opening the box, the system plays a message "medicine due" until the box is opened. (i) Draw a state transition diagram modelling these requirements. Ensure that the transitions are fully labelled. [8 marks] (ii) Describe any ambiguities or clarifications in the requirements, explaining how they relate to your diagram. [3 marks]