MCS 12 , JUNE 2023 QUESTION & ANSWER

 

1. (a) Describe the structure of 8086 microprocessor with the help of a diagram.                                          6

Answer:

The Intel 8086 microprocessor, released in 1978, featured a 16-bit architecture and is a member of the x86 family. Its structure includes:

1. **Data Bus**: It's a 16-bit bi-directional bus used for transferring data between the CPU, memory, and peripherals.

2. **Address Bus**: Also 16-bit, it specifies the memory address for read and write operations.

3. **Control Unit (CU)**: Controls the operation of the entire microprocessor, fetching instructions from memory and executing them.

4. **Arithmetic Logic Unit (ALU)**: Performs arithmetic and logical operations like addition, subtraction, AND, OR, etc.

5. **Registers**: Includes various registers like AX, BX, CX, DX, SI, DI, BP, SP, IP, etc., used for temporary storage of data, addresses, and flags.

6. **Instruction Queue**: Holds instructions fetched from memory, aiding in pipelining.

Here's a simplified diagram:

This illustration gives a basic idea of how the various components are interconnected within the 8086 microprocessor.

(b) What is an instruction cycle ? Explain with the help of a flowchart. 6

An instruction cycle is the basic operational process performed by a computer's central processing unit (CPU) to execute a single instruction. It typically consists of several stages, including fetching, decoding, executing, and sometimes storing the result.

Here's a simplified flowchart illustrating the instruction cycle:

1. **Fetch**: The CPU fetches the next instruction from memory.

2. **Decode**: The fetched instruction is decoded to determine what operation needs to be performed.

3. **Execute**: The CPU carries out the operation specified by the instruction.

4. **Store**: If necessary, the result of the operation is stored in memory or in a register.

This cycle repeats for each instruction in a program, allowing the CPU to process instructions sequentially and perform tasks as directed by the program.

(c) Represent the following numbers using IEEE-754 floating point single precision number format : 

(i) 1010.0001

(ii) -0.0000111

Sure, here are the representations of the numbers in IEEE-754 single precision format:

(i) 1010.0001:

Binary representation: 1.0100001 x 2^3

Sign bit: 0 (positive)

Exponent (biased): 3 + 127 = 130 (in binary: 10000010)

Fraction (significand): 01000010000000000000000 (23 bits)

IEEE-754 representation: 01000001001000010000000000000000

(ii) -0.0000111:

Binary representation: 1.1111 x 2^-4

Sign bit: 1 (negative)

Exponent (biased): -4 + 127 = 123 (in binary: 01111011)

Fraction (significand): 11110000000000000000000 (23 bits)

IEEE-754 representation: 10111101111100000000000000000000

(d) Explain instruction pipeline with the help of a diagram. 4

The instruction pipeline is like an assembly line in a factory where different stages of processing occur simultaneously to execute instructions efficiently. Here's a brief explanation with a simplified diagram:

1. **Fetch**: The instruction is fetched from memory.

2. **Decode**: The fetched instruction is decoded to understand what operation needs to be performed.

3. **Execute**: The operation specified by the instruction is executed.

4. **Write Back**: The result of the executed operation is written back to the appropriate register or memory location.

This process allows multiple instructions to be processed simultaneously, improving overall efficiency. Each stage operates concurrently, enabling a continuous flow of instructions through the pipeline.

(e) What are the different kinds of Interrupts? How does CPU know that an interrupt has occurred? 5

There are three main types of interrupts:

• 1. Hardware Interrupts: These interrupts are generated by external hardware devices, such as a keyboard, mouse, disk drives, or network interface cards, to request attention from the CPU.
• 2. Software Interrupts: These interrupts are triggered by software instructions or conditions, such as a system call or a software error.
• 3. Internal Interrupts: Generated by the CPU itself to indicate exceptional conditions like division by zero or invalid memory access.

The CPU knows an interrupt has occurred through its interrupt handling mechanism. When an interrupt occurs, the CPU pauses its current execution, saves the current state, and jumps to a predefined memory location called an interrupt vector. This vector points to the specific interrupt handling routine, allowing the CPU to handle the interrupt appropriately.

(f) What is DMA ? Explain the functions of DMA. 5

DMA stands for Direct Memory Access. It's a feature of computer systems that allows certain hardware subsystems within the computer to access system memory independently of the central processing unit (CPU).

Functions of DMA:

1. **Data Transfer**: DMA enables efficient data transfer between peripheral devices (like hard drives, network adapters, or GPUs) and system memory without involving the CPU for every byte of data.

2. **Reduced CPU Overhead**: By offloading data transfer tasks from the CPU, DMA reduces CPU overhead, allowing the CPU to focus on executing other tasks, thereby enhancing overall system performance.

3. **Parallel Processing**: DMA allows for parallel processing, enabling simultaneous data transfers between multiple peripherals and memory, which can significantly speed up data-intensive operations.

4. **Increased Throughput**: Since DMA transfers data directly between peripherals and memory, it typically offers higher data transfer rates compared to CPU-managed transfers, leading to increased system throughput.

5. **Efficient Resource Utilization**: DMA helps in efficient utilization of system resources by enabling peripherals to access memory directly, thereby reducing latency and improving system responsiveness.

In short, DMA streamlines data transfer operations by allowing peripherals to access system memory directly, reducing CPU involvement, improving system performance, and enhancing overall efficiency.

(g) Consider a four variable Boolean function :

\[\mathrm{F}=\Sigma(0,4,6,7,8,10,11,15)\]

Minimize this function using K-map and draw the resultant function using logic gates.

(h) Convert decimal number (49.25) \( )_{10} \) into : 

(i) binary

(ii) hexadecimal

(iii) octal