### $($a$)$ Designing the Control Unit of a Simple Hypothetical $16-$bit Microprocessor#### Hardwired Control UnitA hardwired control unit uses fixed logic circuits to control signals and execute instructions. Heres how you can design a hardwired control unit for a $16-$bit microprocessor:$1.**$Instruction Decoder$**$: $-$ Decodes the opcode from the instruction register. $-$ Generates control signals for various stages of instruction execution $($fetch$,$ decode, execute, write$-$back$)\mathrm{.}2.**$Control Signal Generator$**$: $-$ Based on the output of the instruction decoder, generates specific control signals for different components of the microprocessor $($ALU$,$ registers, memory, etc.$)\mathrm{.}3.**$Timing and Control Logic$**$: $-$ Uses a clock to sequence the execution of micro$-$operations. $-$ Ensures that operations are performed in the correct order and at the correct time.#### Example Diagram for Hardwired Control:$```+---------------------+|$ Instruction Register $|+---------------------+|$ v $+---------------------+|$ Instruction $||$ Decoder $|+---------------------+|$ v $+---------------------+|$ Control Signal $||$ Generator $|+---------------------+|$ v $+---------------------+|$ Timing and Control $||$ Logic $|+---------------------+|$ v $+-----------------++-----------------++-----------------+|$ ALU $||$ Registers $||$ Memory $|+-----------------++-----------------++-----------------+```$In this diagram:$-$ The $**$Instruction Register$**$ holds the current instruction.$-$ The $**$Instruction Decoder$**$ decodes the opcode and sends signals to the Control Signal Generator.$-$ The $**$Control Signal Generator$**$ produces the necessary control signals based on the decoded instruction.$-$ The $**$Timing and Control Logic$**$ coordinates the execution of instructions by sequencing the control signals over clock cycles.#### Microprogrammed Control UnitA microprogrammed control unit uses a set of instructions called microinstructions stored in control memory $($microprogram$)$ to generate control signals$\mathrm{.}1.**$Control Memory$**$: $-$ Stores the microprogram which consists of microinstructions. $-$ Each microinstruction specifies a set of control signals for a single micro$-$operation$\mathrm{.}2.**$Microinstruction Register$**$: $-$ Holds the current microinstruction$\mathrm{.}3.**$Microprogram Counter$**$: $-$ Points to the next microinstruction to be fetched from control memory$\mathrm{.}4.**$Control Address Register$**$: $-$ Holds the address of the next microinstruction$\mathrm{.}5.**$Sequencer$**$: $-$ Determines the sequence in which microinstructions are fetched and executed.#### Example Diagram for Microprogrammed Control:$```+-----------------------+|$ Control Memory $||($Microprogram ROM$)|+-----------------------+|$ v $+-----------------------+|$ Microinstruction $||$ Register $|+-----------------------+|$ v $+-----------------------+|$ Microprogram Counter $|+-----------------------+|$ v $+-----------------------+|$ Control Address Reg. $|+-----------------------+|$ v $+-----------------------+|$ Sequencer $|+-----------------------+|$ v