SECR2033 Computer Organization & Architecture

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Questions and Answers

What is the location from which the next instruction is fetched?

941

2941

NUM

302 (correct)

What happens to the PC after fetching the next instruction?

It is reset to 0

It remains the same

It is incremented (correct)

It is decremented

What is the contents of the AC stored in?

Location 941 (correct)

Location 2941

Location 302

What is the instruction MOV AX, NUM an example of?

Indirect cycle Signup and view all the answers

What is the purpose of the fetch cycle?

To retrieve the next instruction Signup and view all the answers

What is the reference source for the examples provided?

William Stallings (2016). Computer Organization and Architecture Signup and view all the answers

How many stages are involved in the instruction processing?

Three Signup and view all the answers

In which stage of the instruction cycle does the processor perform the operation?

Second cycle Signup and view all the answers

What happens to the program execution when a HALT instruction is encountered?

The program execution halts Signup and view all the answers

What is another reason for a program to halt execution besides a HALT instruction?

The machine is turned off Signup and view all the answers

What is the term for the first stage of the instruction cycle?

Fetch cycle Signup and view all the answers

In which stage of the instruction cycle are operands fetched, if required?

First cycle, if indirect Signup and view all the answers

What is the purpose of the third stage of the instruction cycle?

Recognize pending interrupts Signup and view all the answers

What is the term for when a program execution halts due to an unrecoverable error?

Halt Signup and view all the answers

What is the purpose of the Program Status Word (PSW) in a processor design?

To contain status information and condition codes Signup and view all the answers

What type of information do the status flags in the Program Status Word (PSW) reflect?

The outcome of arithmetic and bitwise operations Signup and view all the answers

Which status flag is set when the destination (result) equals zero?

ZF (Zero Flag) Signup and view all the answers

What is the purpose of the Carry Flag (CF) in the Program Status Word (PSW)?

To indicate an overflow in unsigned arithmetic Signup and view all the answers

Which status flag is set when the signed value is out of range?

OF (Overflow Flag) Signup and view all the answers

What is the purpose of the Sign Flag (SF) in the Program Status Word (PSW)?

To indicate that the destination (result) is negative Signup and view all the answers

Which of the following is NOT a common field or flag in the Program Status Word (PSW)?

Instruction Pointer Flag Signup and view all the answers

What is the outcome of arithmetic operations that affect the status flags in the Program Status Word (PSW)?

The status flags reflect the outcome of arithmetic and bitwise operations Signup and view all the answers

Study Notes

Program Status

A register or set of registers, known as the Program Status Word (PSW), contains status information and condition codes.
The ALU has status flags that reflect the outcome of arithmetic (and bitwise) operations.
Common status flags include:
- Zero Flag (ZF): set when the destination (result) equals zero.
- Sign Flag (SF): set when the destination (result) is negative.
- Carry Flag (CF): set when the unsigned value is out of range.
- Overflow Flag (OF): set when the signed value is out of range.

Instruction Processing

Instruction processing consists of three stages:
- Fetch cycle: Fetch the instruction, decode it, and fetch operands if required (indirect).
- Execute cycle: Perform the operation and store results if required.
- Interrupt cycle: Recognize pending interrupts.

Program Execution

Program execution halts only if:
- The machine is turned off.
- Some sort of unrecoverable error occurs.
- A program instruction that halts the computer is encountered.

Example Cycles

Fetch cycle: The next instruction is fetched from the specified location, and the PC is incremented.
Indirect cycle: The contents of the AC are stored in the specified location.
Examples of fetch and indirect cycles are shown in MOV AX, NUM instructions.