a) The designer of a cyclic system wishes to execute the cycle at a fixed interval (e.g. every 10ms). i) Explain why the cycle time cannot be fixed simply by placing a fixed delay at the end of each cycle. ii) Outline the way the SysTick counter can be used to ensure that the cycle time is fixed, including the software components needed. [8 marks] b) It is proposed to use Pulse Width Modulation (PWM) to vary the brightness of several LEDs. i) Explain 'modulation frequency' and 'duty cycle' as they apply to PWM. ii) A PWM peripheral (such as the KL25Z's TPM) has a single 16-bit counter and a modulo value MOD. The counter is driven by a clock of frequency F. The peripheral has multiple channels, each with a channel value CnV. Explain the relationship between these values and a) the modulation frequency and b) the effective voltage applied to an LED connected to one channel. [8 marks] c) An embedded system uses an analogue to digital converter (ADC): i) [UG Only] Explain the purpose of an ADC. Give two examples of physical phenomena that, using an appropriate sensor, would be measured using an ADC. ii) A voltage in the range 0 to 5v is measured using an ADC with a resolution of 12- bits. What value is returned when the voltage is 2v? Your answer may be given as an expression or a number in any base. iii) Explain the main factor that influences the time taken to complete a conversion using a successive approximation ADC. anlal