4.7.3 Processor & Components

• What does the processor send to the CIR?

  Contents of memory location via data bus
• What is the role of the MAR in the processor?

  It loads details of addresses initially
• What does the processor do during the decode phase?

  It takes the instruction from the CIR
• What are the two types of instruction sets?

  RISC and CISC
• What is an instruction set?

  A library of processor commands
• What happens during the execute phase of the processor?

  The processor carries out the instructions
• How do simple and complex instructions differ in execution cycles?

  Simple instructions need one cycle, complex need more
• Where are results of calculations written?

  To a register or memory location
• What are the five registers used in the fetch-execute cycle?

  Status, CIR, PC, MBR, MAR
• What does the status register do?

  Tracks various parts of the computer
• What is the function of the program counter (PC)?

  Stores memory location of next instruction
• What does the memory buffer register (MBR) do?

  Holds data being read or about to be written
• What is the role of the memory address register (MAR)?

  Stores location for data in the MBR
• What is the purpose of the fetch phase?

  PC holds address of next instruction
• What are data transfer operations in operation codes?

  Operations like move, store, load
• What do arithmetic operations include?

  Standard mathematical operations and comparisons
• What is the significance of branch operations?

  Allows non-linear execution of programs
• What does the instruction 'LDR Rd, <memory ref>' do?

  Loads value from memory ref into register d
• What does the instruction 'STR Rd, <memory ref>' do?

  Stores value from register d at memory ref
• What does the instruction 'ADD Rd, Rn, <operand2>' do?

  Adds operand2 to value in register n
• What does the instruction 'SUB Rd, <operand2>' do?

  Subtracts operand2 from value in register n
• What does the instruction 'MOV Rd, <operand2>' do?

  Copies value specified by operand2 into register d
• What does the instruction 'CMP Rn, <operand2>' do?

  Compares value in register n with operand2
• What does the instruction 'B <label>' do?

  Branches to the instruction at label
• What does the instruction 'B <condition><label>' do?

  Conditionally branches to label based on condition
• What does the instruction 'AND Rd, Rn, <operand2>' do?

  Performs AND operation between n and operand2
• What does the instruction 'ORR Rd, Rn, <operand2>' do?

  Performs OR operation between n and operand2
• What does the instruction 'EOR Rd, Rn, <operand2>' do?

  Performs XOR operation between n and operand2
• What does the instruction 'MVN Rd, <operand2>' do?

  Performs NOT operation on operand2
• What does the instruction 'LSL Rd, <operand2>' do?

  Logically shifts left value in register n
• What does the instruction 'LSR Rd, <operand2>' do?

  Logically shifts right value in register n
• What does the instruction 'HALT' do?

  Stops the execution of the program
• What are interrupts in a processor?

  Signals requesting immediate attention from processor
• What happens when a processor receives an interrupt?

  It stops current task and runs associated process
• What are some reasons for interrupts?

  Hardware device signals data or task completion
• What is an Interrupt Service Routine (ISR)?

  A mini program designed to process interrupts
• What effect do interrupts have on the fetch-execute cycle?

  Processor saves registers and identifies interrupt origin
• What happens to low-priority interrupts during ISR execution?

  They are put on hold until ISR finishes
• What is the role of the Arithmetic Logic Unit (ALU)?

  Performs mathematical functions and logic operations
• What types of operations does the ALU perform?

  Mathematical functions and boolean value assignments