11 Arithmetic Logic Unit (ALU)

Question 1

What is the ALU?

Answer 1

Combinational circuit

Question 2

It carries out arithmetic operations such as:

Answer 2

addition • subtraction • multiplication • others

Question 3

It carries out logic operations such as:

Answer 3

AND, OR, NAND, etc • Comparisons (>=, ==, etc

Question 4

It outputs status bits for the Flags/Status register to show:

Answer 4

Carry/borrow from add/subt operations

• Negative results from an operation
• Zero results from an operation

Question 5

ALU symbol

Answer 5

Question 6

The ALU employs the following for its operation:

Answer 6

Two N-bit data inputs, e.g, A and B inputs

• One N-bit data output, e.g., Y output
• A control input that specifies which operation to execute, e.g., F input

Question 7

Example operations performed by the ALU?

Answer 7

Question 8

Opcode

Answer 8

operation code used to let the ALU know what is the required operation.

Question 9

Mnemonics,

Answer 9

easily remembered alphabetic code for the opcode. Mnemonic is used by the Engineer, but by the ALU.

Question 10

machine language

Answer 10

ALU understand machine language

Question 11

What is the status register?

Answer 11

The status register contains information about the state of the microprocessor after an operation has been executed.

The status register allows the program to take a certain action based on a particular condition that resulted from a previous instruction

Question 12

Common flags?

Answer 12

Question 13

The Common instruction set of the microprocessor? ALU or Register operation

Answer 13

Question 14

Instruction Set of the microprocessor

Answer 14

Question 15

What does an instruction set do/contain?

Answer 15

Question 16

Example of 16 bit instruction format

Answer 16

Question 17

Microoperations.

Answer 17

Instructions can be specified with a set of elementary/low-level operations know as Microoperations.

Microoperations are described using Register Transfer Notation (RTN) or Register Transfer Language (RTL).

Question 18

Common microoperations?

Answer 18

LOADX

STOREX

ADDX

JUMPX

Question 19

LOAD X

Answer 19

Question 20

STORE X

Answer 20

Question 21

ADD X

Answer 21

Question 22

JUMP X

Answer 22

Question 23

Assembler

Answer 23

Assembler programs are responsible for this conversion into machine language or machine code

Question 24

Instruction storage format

Answer 24

Question 25

Instruction format with two operands

Answer 25

Question 26

RISC (Reduced Instruction Set Computer): A microprocessor with a small number of simple instructions.

Answer 26

• Large number of general purpose registers
• Simple instructions that execute quickly
• Each instruction performs one operation
• Instructions performs one operation
• Instructions have a fixed size
• Operations are performed between registers

Question 27

CISC (Complex Instruction Set Computer): A microprocessor with a large number of instructions that perform complex computations.

Answer 27

Large number of instructions

Instructions of variable length

A single instruction performs multiple operations

Complex operations required more than one clock cycle

Require multiple clock cycles which slows down the performance

Question 28

Multiplication in RISC?

Answer 28

Question 29

Multiplication in CISC?

Answer 29

Question 30

Abstraction: Assembly language

Answer 30

Assembly language

• Programming language
• Use of mnemonic and operands
• Opcode and address

Question 31

Abstraction levels: Instruction set Architecture

Answer 31

Instruction Set Architecture

• Instructions that a computer is able to perform
• Each instruction is specified by microoperations
• Microoperations are low-level instructions represented with Register Transfer Notation

Question 32

Abstraction Machine language/Code

Answer 32

Machine language/code

• Language compose of 0s and 1s that the computer is able to understandable