INTRODUCTION
ALU (Arithmetic Logic Unit )
An Arithmetic Logic Unit or ALU is a fundamental component of a computer's central
processing unit (CPU) that performs arithmetic and logical operations. It is responsible for
carrying out basic arithmetic operations like addition, subtraction, multiplication, and
division, as well as logical operations such as AND, OR, and NOT. For Arithmetic Operation,
it perform basic arithmetic operations which is addition, multiplication, and division. These
operations are essential for processing numerical data in a computer. Meanwhile Logical
Operations handle the logical operations that involve the manipulations of binary data. The
common logical operations is AND, OR, NOT, EXOR and others. ALU also takes input data
and performs operations on it based on control signals received from the CPU. ALU operate
on individual bits within binary numbers. The example of bitwise operation including shifting
an individual bits to left or right, setting them to 0 or 1. ALU usually work in conjunction with
registers, which are small abd high-speed sotrage locations within the CPU. Register hold data
thata needs to be processsed by ALU temporarily. Modern CPUs often have multiple ALUs
that can operate in parallel, allowing for faster processing of multiple instructions
simultaneously. ALU plays a central role in the executions of instructions and the overall
functioning of a computer’s processor.
Address Decoder
Meanwhile Address decoder is a digital circuit that takes an input address and selects
one or more specific devices or memory locations based in that address. interprets address
information and determines which specific device or component in a digital system should
respond to a particular address. In digital systems, various components such as memory chips,
input/output devices, or other peripheral devices are often connected to a common data bus. To
communicate with a specific device, the system needs a way to select the device using an
address. The address decoder plays a crucial role in directing data to the appropriate
destination.In other word, Address decoding is a crucial component in digital systems,
especially in microprocessor-based architectures, where it enables efficient communication
with various peripherals and memory locations. It helps in managing the address space of the
system and ensures that data is correctly directed to the intended destination.
Input and Output Interface
Input / output or I/O interfacing refers to the connection and communication between
a digital system for example with a microcontroller and microprocessor and between external
devices or perpherals. Input devices such as keyboards, sensors and mice also output devices
such as printers, actuators or display are essential for interaction with the external environment
in a computer system. I/O interfacing serves as the exchanger of data between the central
processing unit or CPU and these external devices. The CPU communicates with external
devices using specific addresses and control signals. I/O interfacing often involves the use of
special ports and registers. These are memory locations or specific addresses designated for
communication with external devices. Input ports receive data from external devices, while
output ports send data to them. A classic and common example of I/O interfacing is the
connection between a microcontroller and a simple digital input device, such as a push-button
switch or interfacing a digital camera with a computer.
ARITHMETIC LOGIC UNIT ( ALU )
Basic Structure of ALU
The integer operand : ALU has a total three data buses, two of them are input buses (A and
B bus) and the remaining is output bus (Y bus). Each of these buses carries one binary integer
number value. Size of these buses is the same as the native word size of the external circuitry.
The Opcode : Opcode bus carries operation selection code (enumerated value of operation) to
ALU. In simple terms Opcode tells ALU which operation is to be performed.
The Status : status are individual signals which carry information about the result of current
ALU operation.
Block Diagram of a 4-bit ALU
The basic example of ALU operations
1) State the result of A + B and A – B , if given A = 0111 0101 , B = 0001 1011
i)
A+ B
0111 0101
+ 0001 1011
1001 0000
ii)
The result of A + B = 1001 0000 in
binary.
A– B
0111 0101
- 0001 1011
0101 1010
The result of A - B =0101 1010 in
binary.
INPUT AND OUTPUT (I/O) INTERFACING
Below is the input output interface ports that ususallly or the main input and output ports :
Input-Output Interface is used as an method which helps in transferring of information
between the internal storage devices. A peripheral device is that which provide input and
output for the computer, it is also called Input-Output devices.
Example of :
1) Input Devices
A keyboard and and mouse that provide Input to the computer are called input devices.
2) Output Devices
A monitor and printer that provide output to the computer are called output devices.
This is the connection of I/O bus to input-output devices :
I/O Interface for an Input :
Example : KEYBOARD INTERFACE
-
Each key on the keyboard is assigned a unique keycode. When a key is pressed, the
keyboard's internal controller generates a keycode corresponding to the pressed key.
For wired keyboards, such as those using USB or PS/2 interfaces, the generated
keycodes are transmitted to the computer over the physical cable.
I/O Interface for an Output :
Example : DISPLAY INTERFACE
-
-
The display interface is the vital for transmitting video signals from the device to the
monitor or screen, allowing users to visualize digital content.
One of the common display interface is HDMI (High-Definition Multimedia
Interface). HDMI is a widely used digital interface for transmitting high-definition
audio and video signals. It supports a wide range of resolutions and can carry both
audio and video data on a single cable. HDMI is commonly used in TVs, monitors,
and multimedia devices.
The display interface is the easiest task because no interrupt concept apply since
screen are always ready for output.
On display interface, CPU will take this action :



Takes the character and copies them to screen memory at the location of the
current cursor.
Updated the cursor position
And if necessary, it wraps or scrolls the screen.
CONCLUSION
In conclusion, the combination of the Arithmetic Logic Unit or ALU, address decoder, and
I/O interface form the backbone of a computer operating system or ot system, or can be say
that ALU, Address Decoder and I/O interface are the main roles in its functionality and
overall performance of a computer system.
It is because the ALU serves as the computational powerhouse or a high-capacity processing
unit, executing arithmetic and logical operations that are fundamental to processing the
information within the system. It’s efficiency directly influences the speed and capability of
the computer in handling complex tasks. The ALU's effectiveness in swiftly and accurately
executing arithmetic and logical operations directly determines how well the computer can
handle intricate and complex tasks or can be say that the ALU's efficiency is a key factor in
determining the system's ability to process complex operations at a desirable speed and with
optimal performance. That’s what make it is the most important or the most critical
component of the Central Processing Unit ( CPU ).
Then the address decoder acts as a crucial bridge which is a vital connecting element that
facilitates communication or interaction between two essential components of a system.
between the CPU and memory subsystem. So the address decoder plays a critical role in
connecting and enabling efficient data exchange between these fundamental components,
ensuring the smooth functioning of a computer system. It interprets memory addresses and
facilitates the seamless retrieval and storage of data, ensuring that the right information is
accessed at the right time. The accuracy and speed of the address decoder significantly impact
the overall efficiency and responsiveness of the computer.
At the same time, the I/O interface acts as the interface between the computer and external
devices or serves as the connection point between a computer system and external devices
such as keyboards, mice, monitors, and other external devices, which enabling
communication and data transfer between the system and peripherals. I/O interface is the
point of interaction and communication between the computer and external devices. This
component is instrumental in facilitating the interaction with the outside world, allowing users
to input data that enables users to provide information to the computer system, such as typing
on a keyboard, clicking with a mouse ,to receive output or facilitates the transfer of
information from the computer to the user, allowing for the display of results, graphics, or any
other output on devices like monitors or printers , and connect to various devices where
interface serves as a connection point for a range of external devices.
When these three component works together, these component form a symbiotic relationship
that enables a computer to execute instructions such as carry out instructions, which are sets
of operations or tasks that the computer performs to accomplish specific goals, to process data
contribute to the processing of data, involving tasks like calculations, comparisons, and
manipulations of information, and interact with its environment. In essence, the
interconnected components create a harmonious and interdependent system, empowering the
computer to function cohesively, execute tasks, handle data, and engage with the external
world in a meaningful way. The cooperative action of these different components which is the
ALU, address decoder, and I/O interface is crucial for achieving optimal performance,
responsiveness, and versatility in computing systems.