$1.$ The ARM processor is interfaced with two sensors utilized for object detection, and a control unit that enables transfer of data in$/$out of memory with minimal interference from the processor. When the processor is executing the main program, a timer is triggered to count from $100$ to $0.$ In this case, when the counter reaches $50,$ the first sensor is triggered to detect an object, and when an object is detected the processor utilizes information acquired from the sensor to calculate the distance, and store the results in memory, then the counter continues decrementing. However, when the counter reaches $0$ the second sensor is triggered to detect an object, and when an object is detected the control unit transfers data from the sensor to memory. Once data from the second sensor is stored in memory a new value is loaded into the counter to enable the counter to re$-$start the process again $[34$ Marks$]$

f$)$ Name and explain the mode of operation of the control unit, also state the disadvantage of the mode $[3$ Marks$]$

g$)$ Name and explain three sets of instructions used to move data from the first sensor in$/$out of memory and registers. Also name and explain the addressing mode used when these instructions are executed $[9$ Marks$]$