Computer Architecture: Fetch Cycle Registers
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Questions and Answers

What does the instruction decoding process involve?

  • Performing arithmetic calculations
  • Setting the instruction cycle code
  • Generating a sequence of micro-operations based on the opcode (correct)
  • Loading data into memory

The indirect cycle is always followed by the fetch cycle.

False (B)

What are the four states represented by the instruction cycle code (ICC)?

Fetch, Indirect, Execute, Interrupt

The component responsible for performing arithmetic and logic operations is called the __________.

<p>ALU</p> Signup and view all the answers

Match the following processor components with their functions:

<p>ALU = Performs arithmetic and logic operations Registers = Stores data temporarily Internal Data Paths = Move data within the processor Instruction Cycle Code (ICC) = Indicates current state of instruction cycle</p> Signup and view all the answers

Which micro-operation occurs first when executing an ADD instruction?

<p>MAR  (IR(address)) (D)</p> Signup and view all the answers

Registers are used for permanent storage of data within the processor.

<p>False (B)</p> Signup and view all the answers

What sequence of micro-operations would likely follow the loading of the address into the MAR?

<p>MBR  Memory, R1  (R1) + (MBR)</p> Signup and view all the answers

What is the role of control signals in a processor?

<p>They act as commands issued by the control unit to manage component activities. (B)</p> Signup and view all the answers

Control words are collections of bits used to activate specific processor control lines.

<p>True (A)</p> Signup and view all the answers

What is the purpose of the system bus in a processor?

<p>The system bus serves as a communication pathway allowing the control unit to interact with memory and I/O modules.</p> Signup and view all the answers

The control unit directs the flow of data and operations using _____ signals.

<p>control</p> Signup and view all the answers

Match the following components with their functions:

<p>Control Unit = Issues control signals System Bus = Communication pathway Control Word = Activates specific control lines Control Signals = Manage component activities</p> Signup and view all the answers

What is the primary function of the control unit in a processor?

<p>Overseeing and controlling operations (D)</p> Signup and view all the answers

The control signals generated by the control unit are only used for external communication.

<p>False (B)</p> Signup and view all the answers

Name one method used to implement the tasks of the control unit.

<p>Hardwired control or microprogrammed control.</p> Signup and view all the answers

The control unit determines the ________ of micro-operations.

<p>sequencing</p> Signup and view all the answers

Which of the following is NOT a type of control signal?

<p>Memory allocation signal (A)</p> Signup and view all the answers

Match the types of control signals with their functions:

<p>ALU activation signal = Instructs the ALU to perform functions Data path signal = Controls the internal flow of data External bus signal = Coordinates communication with external devices</p> Signup and view all the answers

Which component communicates with external modules using external data paths?

<p>System Bus (B)</p> Signup and view all the answers

Describe one function of the control unit related to instruction execution.

<p>Activating the necessary control signals to execute each micro-operation.</p> Signup and view all the answers

What is the primary role of clock pulses in the control unit's operations?

<p>To provide a regular timing mechanism (B)</p> Signup and view all the answers

The control unit has direct access to the data being processed.

<p>False (B)</p> Signup and view all the answers

What does the control unit rely on to make decisions about controlling operations?

<p>Pre-programmed knowledge and predefined rules.</p> Signup and view all the answers

The control unit is considered _____ because it operates with limited visibility of actual results.

<p>minimal</p> Signup and view all the answers

Match the function with its corresponding description:

<p>Clock Pulses = Provide timing for events Control Unit = Orchestrates instruction execution Micro-operations = Basic tasks performed during processing Instructions = Commands for the processor</p> Signup and view all the answers

Which register holds the address of the next instruction to be fetched?

<p>Program Counter (PC) (D)</p> Signup and view all the answers

What is one significant aspect of the control unit's operation?

<p>Issues control signals (D)</p> Signup and view all the answers

The control unit's minimal access to data limits its functionality in a computer.

<p>False (B)</p> Signup and view all the answers

The Memory Buffer Register (MBR) contains the address of the next instruction to be executed.

<p>False (B)</p> Signup and view all the answers

How do clock pulses contribute to the instruction cycle?

<p>They ensure orderly progression and prevent conflicts.</p> Signup and view all the answers

What is the first step in the Fetch cycle?

<p>Move the address of the next instruction from the program counter (PC) to the memory address register (MAR).</p> Signup and view all the answers

In the Indirect cycle, the instruction's address field is first transferred to the _______.

<p>MAR</p> Signup and view all the answers

Match the register with its function:

<p>MAR = Holds the address of memory for read/write operations MBR = Contains value to be stored or last value read PC = Holds the address of the next instruction IR = Holds the last instruction fetched</p> Signup and view all the answers

What happens during the Interrupt cycle?

<p>The address of the interrupt routine is stored in the PC. (B)</p> Signup and view all the answers

The Execute cycle has a fixed sequence of micro-operations.

<p>False (B)</p> Signup and view all the answers

What must occur if an instruction specifies an indirect address?

<p>An indirect cycle must precede the execute cycle.</p> Signup and view all the answers

What is the primary role of control signals emitted by the control unit?

<p>To initiate specific micro-operations (A)</p> Signup and view all the answers

The control unit does not need to track its position in the instruction cycle.

<p>False (B)</p> Signup and view all the answers

What signals does the control unit send to read a word from memory into the MBR?

<p>A control signal that opens gates for the MAR onto the address bus, a memory read control signal on the control bus, a signal for data bus storage in MBR, and signals to increment the PC.</p> Signup and view all the answers

The control unit opens the gates between the PC and the _____ during the fetch cycle.

<p>MAR</p> Signup and view all the answers

Match the following components with their functions during the fetch cycle:

<p>PC = Holds the address of the next instruction MAR = Stores the address to be accessed in memory MBR = Holds the data read from memory IR = Holds the instruction that is currently being executed</p> Signup and view all the answers

What happens first in the fetch cycle?

<p>The contents of the PC are transferred to the MAR (B)</p> Signup and view all the answers

The control unit can perform indirect cycles without examining the IR.

<p>False (B)</p> Signup and view all the answers

How does the control unit maintain knowledge of its position in the instruction cycle?

<p>It uses its internal state information to track the current stage of the instruction cycle.</p> Signup and view all the answers

Flashcards

Instruction Decoding

The process of converting an instruction's opcode into a sequence of micro-operations.

Micro-operations

A sequence of low-level operations that the CPU performs to complete an instruction like addition or memory access.

Instruction Register (IR)

A register that temporarily stores the current instruction being processed.

Memory Address Register (MAR)

A register that holds the memory address for the next data to be fetched.

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Memory Buffer Register (MBR)

A register that temporarily stores data fetched from memory.

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General Purpose Register (R1)

A register that holds a value, like a variable, for use in calculations and operations.

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Arithmetic Logic Unit (ALU)

A dedicated circuit within the CPU that performs arithmetic and logic operations on data.

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Internal Data Paths

Internal lines within the CPU that transfer data between different components, such as registers and the ALU.

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Control Unit

The brain of the CPU, responsible for overseeing and coordinating all operations.

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Sequencing

The control unit's task of determining the order in which micro-operations should be executed.

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Execution

The control unit's task of activating the necessary control signals to execute each micro-operation.

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Hardwired Control

A method of control where logic circuits directly generate control signals, offering speed and efficiency.

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Microprogrammed Control

A method of control where microinstructions stored in memory define the sequences of operations, providing flexibility.

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Control Signals

Electrical signals generated by the control unit to control the actions of various components within the CPU.

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System Bus

A pathway used by the control unit to communicate with external components, like memory and I/O modules.

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Control Word

A set of bits used to activate specific control lines in the processor, determining which micro-operations to execute.

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Control Memory

A storage location that holds control words, allowing the control unit to access and interpret them for executing micro-operations.

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Fetch Cycle

The step in the instruction cycle where the CPU retrieves the next instruction from memory. This is like fetching a recipe from the cookbook to start cooking.

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Control Unit State

The control unit uses its internal state information to keep track of its position in the instruction cycle, allowing it to activate the appropriate control signals for each step. This is like a chef following a recipe step-by-step.

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What is the role of the control unit?

The control unit is the brain of the computer, responsible for interpreting instructions and orchestrating the execution of tasks.

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Why is timing important for the control unit?

It's essential for the control unit to use a clock to coordinate micro-operations, ensuring smooth and accurate execution of instructions.

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How do clock pulses ensure coordination within the control unit?

Clock pulses are like a metronome, creating a regular beat. They synchronize actions within the CPU, preventing conflicts and ensuring that every component operates in harmony.

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What does the control unit do with instructions?

The control unit's job is to read instructions and send signals to other components to perform the necessary operations.

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How does the control unit manage with limited information?

Despite its minimal access to data, the control unit directs the computer's entire operation by issuing control signals to various components.

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What information does the control unit know and not know?

The control unit has knowledge of the instructions and how they should be executed, but it doesn't have access to the actual data being processed.

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How does the control unit make decisions without knowing the data?

The control unit uses pre-programmed instructions and rules to make decisions. It doesn't need to directly observe the data because it already knows how different instructions should be executed.

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Program Counter (PC)

A register that holds the address of the next instruction to be fetched from memory. It acts as a pointer to the program's flow.

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Execute Cycle

The part of the instruction cycle that performs the actual operation specified by the instruction, such as adding, subtracting, or moving data. The specific steps vary based on the instruction's opcode.

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Indirect Addressing

An addressing mode where the address field of an instruction points to another memory location that contains the actual address of the operand. It's like a treasure map leading to another map.

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Interrupt Cycle

The process the CPU uses to handle an interrupt, which is a signal that requires the CPU to temporarily stop its current task to handle a more urgent event. It involves saving the current state of the CPU and transferring control to an interrupt service routine.

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Study Notes

Fetch Cycle Registers

  • Memory Address Register (MAR): Connects to the system bus's address lines, specifying memory address for read/write operations.
  • Memory Buffer Register (MBR): Connects to the data lines of the system bus, containing the value to be stored in memory or the last value read.
  • Program Counter (PC): Holds the address of the next instruction to be fetched.
  • Instruction Register (IR): Holds the last fetched instruction.

Fetch Cycle Steps and Micro-operations

  • Step 1: The address of the next instruction is moved from the Program Counter (PC) to the Memory Address Register (MAR).
  • Step 2: The instruction is read from memory (at the address in MAR) and stored in the Memory Buffer Register (MBR). Simultaneously, the Program Counter (PC) is incremented to prepare for the next instruction fetch.
  • Step 3: The instruction is moved from the Memory Buffer Register (MBR) to the Instruction Register (IR).

Indirect Cycle Steps

  • If an instruction specifies an indirect address, an indirect cycle precedes the execute cycle.
  • The address field of the instruction is transferred to the Memory Address Register (MAR).
  • The address of the operand is fetched using the MAR.
  • The address field of the Instruction Register (IR) is updated from the Memory Buffer Register (MBR), changing it from indirect to direct.
  • The IR is now ready for the execute cycle.

Interrupt Cycle Steps and Micro-operations

  • To handle an interrupt, the processor saves the contents of the Program Counter (PC) into the Memory Buffer Register (MBR).
  • The memory buffer address is stored in the Memory Address Register (MAR).
  • The control unit loads the interrupt routine address into the Program Counter (PC).
  • Then, the CPU processes the interrupt and continues with the instruction cycle.

Execute Cycle Differences

  • The execute cycle doesn't have a fixed micro-operation sequence like the fetch, indirect, and interrupt cycles, due to the variety of opcodes.
  • The control unit decodes the opcode to determine the specific sequence of micro-operations.
  • This dynamic sequence is dependent on the instruction currently being executed

Processor Functional Elements

  • Arithmetic Logic Unit (ALU): Performs arithmetic and logical operations.
  • Registers: Temporary storage for data inside the processor.
  • Internal Data Paths: Pathways for data transfer between internal components.
  • External Data Paths: Connections linking registers to external devices (e.g., memory).
  • Control Unit: Manages and directs all operations within the processor.

Control Unit Tasks

  • Sequencing: Determines the order of micro-operations.
  • Execution: Activating the necessary control signals for each micro-operation.

Control Signals

  • Control signals are electrical signals activating ALU functions, controlling data pathways, and interacting with external interfaces.
  • Data path, ALU, system bus control lines are different types.
  • Control signals control data transfers and operations inside the processor.

Control Unit's Fetch Cycle

  • The control unit monitors cycles and maintains an internal state to know its position within the instruction cycle.
  • The control unit emits signals to perform tasks like reading from memory, updating the Program Counter (PC), and transferring data.

Control Unit in a Computer

  • The control unit manages and synchronizes all processor components and operations.
  • It ensures that micro-operations happen at correct times, preventing conflicts.
  • It acts as the central command center.

Control Unit's Decision-Making

  • Control unit decisions are made without physically observing results but based on pre-programmed logic.
  • Understanding instruction sets and expected results drive control signal generation to initiate the correct micro-operations necessary for proper execution.

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Description

Explore the essential components of the fetch cycle in computer architecture, including the Memory Address Register (MAR), Memory Buffer Register (MBR), Program Counter (PC), and Instruction Register (IR). This quiz covers their functions, steps involved in the fetch cycle, and how they interact during instruction fetching in a CPU. Test your knowledge on the fundamental aspects of CPU operations.

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