Test: Machine Instructions & Addressing Modes - Electronics and Communication Engineering (ECE) MCQ

Concept:

Option 1: Parallelism is high in the horizontal microprogrammed control unit as compared to a vertical microprogrammed control unit.

True, Parallelism is high in horizontal microprogramming as several operations on different registers can be performed simultaneously.

Option 2: Hardwired control unit is slower compared to the microprogrammed control unit.

False, a Hardwired control unit is faster as compared to the microprogrammed control unit as there won’t be a delay of fetch, decoding, and executing the control instructions in the case of the hardwired control unit.

Option 3: In 2’s complement sum carry flag and overflow are the same.

False, In unsigned numbers, carry out is equivalent to overflow. But in two's complement, carry out tells you nothing about overflow.

Option 4: In 2’s complement sum if the sum of two negative numbers yields a positive result, the sum has overflowed.

True, the Following are the rules for detecting overflow in a two's complement sum:

• If the sum of two positive numbers yields a negative result, the sum has overflowed.
• If the sum of two negative numbers yields a positive result, the sum has overflowed.

Otherwise, the sum has not overflowed.

Hence the correct answer is option 1 and option 4.

The correct answer is SSID.

Concept:

SISD:

• SISD stands for single instruction, single data
• SISD is a uniprocessor machine capable of executing a single instruction, which operates on a single data stream.
• Von Neumann computer architecture is SISD

SIMD:

• SIMD stands for Single Instruction, Multiple data
• A single operation executes simultaneously on multiple elements of data.

MIMD:

• MIMD stands for multiple instructions, multiple data
• Separate instruction streams, each with its own flow of control, operate on separate data.

MISD:

• MISD stands for multiple instructions, single data
• In MISD many functional units perform different operations on the same data.

So option 1 is the correct answer.

RISC (reduced instruction set computer) is a microprocessor that is designed to perform smaller number of instructions so that it can operate faster. RISC instruction sets are simple. RISC instruction takes only one clock cycle per instruction to execute.

Difference between Microprogrammed Control Unit and Hardwired Control Unit

Therefore, a micro programmed control unit facilitates easy implementation of a new instruction

In assembly language mnemonics are used to represent operation codes.

Opcodes (operation codes) are represented by abbreviations, called mnemonics that indicate the operation.

Mnemonic codes:

• Mnemonic codes are the codes that can be remembered comparatively easily and that aids its user in recalling the information it represents.
• Mnemonics codes are widely used in computer programming and communication system operations to specify instructions.

Examples:

ADD       Add

SUB        Subtract

MUL      Multiply

DIV         Divide

LOAD     Load data from memory

STOR     Store data to memory

Concept:

RISC stands for reduced instruction set computing, which means processing the information using the microprocessors that execute the simplest instructions or fewer instructions in a small amount of time. 

Explanation:

In most RISC processors, hardwired control is found. RISC architecture uses separate instruction and data caches and different access paths. Some points about the RISC processor are :

• Simple instructions taking one cycle.
• Instructions are executed by hardware.
• Fixed format for the instructions.
• Stores only essential instructions and enhances the speed.
• Few addressing modes.
• Highly pipelined and multiple register sets.

Diagram:

Accumulator:

• An accumulator acts as a temporary storage location to hold an intermediate result in mathematical and logical calculations.
• Accumulator is a type of register present in a CPU (Central Processing Unit).
• It works as a temporary storage location that keeps an intermediate value in logical and mathematical calculations.
• Intermediate results of execution are progressively stored to the accumulator, replacing the previous value.

Instruction Register:

• An IR (Instruction Register) saves machine instruction that is currently under execution. It is a register that sits at the top of the memory hierarchy.
• A variety of registers fulfils different operations in a central processing unit (CPU) – the function of the IR is to keep that currently stacked instruction for use.

Program counter:

• A PC (program counter) is a CPU register which has the address stored for the next instruction to be processed from memory.
• It is a digital counter required for quicker execution of tasks as well as to keep track of the current execution point. 

Memory Address Register:

• The MAR (Memory Address Register) is the register in the control unit that holds the address of a register to receive or store from or to the storage.
• The Memory Address Register is half of an interaction between a microprogram and storage.

Concept:-

A register capable of shifting its binary information either to the right or the left is called a shift register.

Key Points

• A unidirectional shift register is one that allows data to be shifted just in one way, whereas a bidirectional shift register allows data to be shifted in both directions.
• In calculators, computers, and data processing systems, a shift register is a digital memory circuit.
• Numerous flip-flops are required to store multiple bits of information. The register is a collection of flip-flops that are used to hold and save binary data.

The instruction is using immediate addressing mode hence the value is stored in the location 45 is added.

In this addressing mode, the value of the register serves as another memory location and hence we use pointers to get the data.