Lecture 11 Flashcards
What are the main subsystems of the CPU?
Control Unit (CU)
Arithmetic Logic Unit (ALU)
Registers
How does data flow between the CPU, memory, and I/O devices?
Program and data are fed into the computer through the input unit and stored in memory.
Control Unit fetches instructions from memory and stores them in registers.
Control Unit decodes instructions and issues control signals.
Instructions are executed by the ALU, and results are stored in memory or registers.
Results are output through the output unit.
What are the steps of the Instruction Cycle?
Fetch instruction: Control Unit sends content to Memory Address Register (MAR) and performs read operation.
Decode instruction: Control Unit analyzes the Operation Code (OPCODE).
Operand address calculation and fetch: Control Unit fetches operand from registers and supplies to ALU.
Execute instruction: ALU performs arithmetic or logic operations.
Result store: Control Unit stores result in memory or registers.
What are the functions of the Control Unit?
Directs all operations of the processor.
Manages resources in the computer system.
Instructs memory, ALU, and I/O devices on how to respond to program instructions.
Generates timing and control signals.
Instructs ALU on operations to perform on data.
Define data path and control path in processor design.
Data Path: The hardware that performs data processing operations (e.g., ALU, registers).
Control Path: The hardware that generates control signals to direct operations (e.g., Control Unit).
What are the two types of Control Unit design?
Hardwired Control Unit:
Uses physical components like gates, flip-flops, decoders.
Generates control signals using fixed logic circuits.
Difficult to modify.
Microprogrammed Control Unit:
Uses programming approach with micro-instructions in control memory.
Generates control signals through a microprogram.
Easy to modify and flexible.
Describe implementing data path using arithmetic instructions.
Example 1: A = B + C
Example 2: D = A - C
Use 16-bit registers to store values and perform operations.
Compare Hardwired and Microprogrammed Control Units based on speed.
Hardwired: Faster fetching and execution of instructions.
Microprogrammed: Slower speed due to fetching instructions from control memory.
Compare Hardwired and Microprogrammed Control Units based on cost.
Hardwired: More costly to build.
Microprogrammed: Less costly; only requires micro-instructions program.
Compare Hardwired and Microprogrammed Control Units based on modification ease.
Hardwired: Difficult to modify, may require redesign of circuits.
Microprogrammed: Easy to modify at the instruction level.
Compare the handling of complex instructions in Hardwired and Microprogrammed Control Units.
Hardwired: Unable to handle complex instructions due to circuit complexity.
Microprogrammed: Can handle complex instructions.
What are the application areas for Hardwired and Microprogrammed Control Units?
Hardwired: Suited for Reduced Instruction Set Computer (RISC).
Microprogrammed: Suited for Complex Instruction Set Computer (CISC).
Describe the role of control signals in processor operations.
Determine the sequence of operations performed by the processor.
Define timing and type of operations to be executed.
What is the importance of the Program Counter (PC) in program execution?
PC contains the memory address where the program begins.
Increments to point to the next instruction after fetching the current one.
Explain the significance of the Memory Address Register (MAR).
Holds the memory address of data/instructions to be fetched or stored.
Used in the fetch phase of the instruction cycle.
