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CPU Control Unit Concepts
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CPU Control Unit Concepts
CPU Control Unit Concepts
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1
Question
What are the control signal codes for each time slot (T1-T4)?
Answer
T1 for fetching is 1000, T2 for decoding is 0100, T3 for executing is 0010, and T4 for write back is 0001.
2
Question
What is the primary responsibility of the control unit in a CPU?
Answer
The control unit is responsible for the fetch, decode, execute instructions, and controlling data going to and coming from the main memory.
3
Question
What role does the Address Sequencer play in a microprogrammed control unit?
Answer
The Address Sequencer determines the next address for instruction fetching and manages aspects like incrementing the CAR and handling conditional branches.
4
Question
What is an active control signal?
Answer
Active control signals are the outputs from the control unit that manage operations of registers, the ALU, and memory.
5
Question
What constitutes the CPU datapath?
Answer
The CPU datapath consists of the ALU, Register Controls, data Adders, multipliers, dividers, and Shifters.
6
Question
What does the 3 bits opcode go into for decoding?
Answer
The 3 bits opcode goes into an 3-to-8 decoder, with each outputted signal triggering different circuits for operations.
7
Question
What is the purpose of the CROM in a microprogrammed control unit?
Answer
The CROM holds the instructions that are fetched and decoded to generate control signals.
8
Question
How is the opcode processed in the MARIE Architecture during direct mapping?
Answer
The opcode indicates a specific address location directly in CROM for mapping.
9
Question
What types of memory are mentioned in relation to microprogrammed control units?
Answer
Dynamic RAM memory and Static ROM memory are mentioned.
10
Question
What happens during the decoding step in a microprogrammed control unit?
Answer
During the decoding step, the opcode is processed through an 3-to-8 decoder, which produces control signals that direct the operation of other circuits.
11
Question
What is a subroutine in the context of program execution?
Answer
A subroutine is a program used by another program to perform a specific task, requiring branching to execute.
12
Question
What does the control unit generate to direct the flow of data?
Answer
The control unit generates control signals to direct the flow of data between the processor and other devices for data transfer.
13
Question
What happens when an instruction is fetched from the CROM?
Answer
The instruction is decoded to generate control signals that will direct the subsequent operations of the control unit.
14
Question
What roles do the Fetch unit, Decode unit, Execute unit, and Write back unit play in the control unit?
Answer
The Fetch unit retrieves the next instruction, the Decode unit interprets the instruction, the Execute unit performs the operation, and the Write back unit updates the results into memory.
15
Question
What does a microprogrammed control unit rely on?
Answer
A microprogrammed control unit relies on a microcode, which is a language for fetch, decode, execute processes to generate control signals stored in a control memory (CROM).
16
Question
How does the control unit coordinate execution units like the ALU?
Answer
The control unit coordinates execution units by using the decoded opcode to direct operations.
17
Question
What is the order of operations for the control unit in a single clock cycle?
Answer
The order of operations is: Fetch, Decode, Execute, Write Back.
18
Question
What are the characteristics of a hardwired control unit?
Answer
A hardwired control unit uses logic gates to automatically generate control signals, is fast but not reconfigurable, and is more suitable for RISC machines.
19
Question
What types of branches can be executed based on special bits?
Answer
Conditional branches, unconditional branches, and subroutine returns can be executed based on special bits.