8085 Architecture | Learn Intel 8085 Microprocessor Architecture Step - By - Step

Summary

This tutorial offers an in-depth exploration of the Intel 8085 microprocessor architecture, ideal for computer science students. It covers the 8085's history, technical specifications, and its five major functional units, including the memory unit, ALU, instruction decoder, timing and control unit, and interrupts. The video simplifies complex concepts, such as the instruction cycle and flag register, and explains the 8085's bus architecture, making it easier to grasp foundational microprocessor concepts.

Takeaways

• 😀 The Intel 8085 microprocessor was one of the first 8-bit processors launched by Intel in 1976 and remains in use today.
• 📚 Studying the 8085 architecture is fundamental for computer science students as it provides a basis for understanding more complex microprocessor architectures.
• 💡 The microprocessor's main function is to execute programs, which are sets of instructions directing the CPU to perform operations.
• 🔍 The instruction cycle of the CPU includes three steps: fetch, decode, and execute, which are repeated to perform program instructions.
• 🔧 The 8085 microprocessor architecture can be broken down into five major functional units: memory unit, ALU, instruction decoder, timing and control unit, and interrupts and serial communication unit.
• 🔢 The 8085 is an 8-bit processor with a 40-pin configuration, operating on a +5V supply and available in 3.5 MHz and 6 MHz execution speed variants.
• 📈 It has an 8-bit data bus and a 16-bit address bus, allowing it to address up to 64 kilobytes of memory.
• 🔑 The 8085 features 6 general-purpose 8-bit registers (B, C, D, E, H, L) and special-purpose registers for specific functions during instruction execution.
• 🚀 The accumulator, part of the ALU, is used to store operands and perform arithmetic and logical operations as per the decoded operation code.
• 📊 The flag register, or program status word (PSW), is an 8-bit register indicating the CPU status after ALU operations, using flags like carry, auxiliary carry, sign, parity, and zero.
• 🔄 The timing and control unit generates clock pulses and control signals to synchronize the operations of internal components and manage external hardware devices.

Q & A

What is the 8085 microprocessor and when was it launched by Intel?

The 8085 microprocessor is an 8-bit processor launched by Intel Corporation in 1976. It was one of the first 8-bit processors and is still in use today in many devices.

Why is it important for computer science students to study the 8085 architecture?

Studying the 8085 architecture is important for computer science students as it helps them understand foundational concepts necessary to study more complex microprocessor architectures and how CPUs work.

What is the basic operation of a CPU called?

The basic operation of a CPU is called the instruction cycle, which includes fetch, decode, and execute operations.

What are the five major functional units of the 8085 microprocessor?

The five major functional units of the 8085 microprocessor are the memory unit (register unit), the arithmetic and logic unit (ALU), the instruction decoder and machine cycle encoder unit, the timing and control unit, and the interrupts and serial communication unit.

What is the purpose of the Program Counter (PC) register in the 8085 architecture?

The Program Counter (PC) register is a 16-bit special purpose register used to store the address of the instruction that needs to be fetched from memory.

What is the role of the Accumulator register in the 8085 processor?

The Accumulator register is part of the Arithmetic and Logic Unit (ALU) and stores the operand part of the instruction format for performing arithmetic and logical operations.

What does the Flag Register indicate in the 8085 architecture?

The Flag Register, also known as the Program Status Word (PSW), is an 8-bit special purpose register that indicates the status of the processor after each ALU operation, such as carry, sign, zero, auxiliary carry, and parity.

What are the functions of the Timing and Control Unit in the 8085 microprocessor?

The Timing and Control Unit generates clock pulses and control signals to synchronize the operations of the CPU's internal components and manage the operations of various hardware devices connected to the system.

How many types of interrupts does the 8085 architecture support?

The 8085 architecture supports eight software interrupts and five hardware interrupts.

What are the three main components of the 8085 bus architecture?

The three main components of the 8085 bus architecture are the address bus, the data bus, and the control bus.

What is the significance of the data bus in the 8085 architecture?

The data bus in the 8085 architecture is an 8-bit bi-directional bus used to transfer data between the CPU and the main memory RAM during memory read and write operations.

Outlines

00:00

📚 Introduction to Intel 8085 Microprocessor Architecture

This paragraph introduces the Intel 8085 microprocessor, one of the first 8-bit processors launched by Intel in 1976. It emphasizes the importance of studying the 8085 architecture for computer science students as foundational knowledge for understanding more complex architectures. The video tutorial aims to simplify the learning process by explaining the architecture, its functional components, and the interaction between these units. The microprocessor's role as the 'brain' of the computer system is highlighted, along with the basic operation of fetching, decoding, and executing instructions. The paragraph sets the stage for a detailed exploration of the 8085's architecture.

05:02

🔍 Detailed Exploration of 8085 Microprocessor Components

This paragraph delves into the technical features of the 8085 microprocessor, including its 8-bit data bus, 16-bit address bus, and 40 pins. It operates at 3.5 and 6 megahertz and has a stack pointer and six 8-bit general-purpose registers (B, C, D, E, H, L). The paragraph also discusses the processor's support for software and hardware interrupts. The focus then shifts to the five major functional units of the 8085: the memory or register unit, the arithmetic and logic unit (ALU), the instruction decoder and machine cycle encoder unit, the timing and control unit, and the interrupts and serial communication unit. Each unit's role in the microprocessor's operation is explained, providing a comprehensive overview of the 8085's internal workings.

10:02

🚀 Understanding CPU Registers and Their Functions

The third paragraph focuses on the various CPU registers within the 8085 microprocessor, explaining their types and functions. General-purpose registers are used for temporary data storage, while special-purpose registers serve specific functions. The program counter (PC), instruction register (IR), and accumulator are highlighted as key special-purpose registers. The accumulator is part of the ALU, which performs arithmetic and logical operations. The flag register, also known as the program status word (PSW), is detailed, explaining its role in indicating the CPU's status after ALU operations. The five flags used in the 8085 processor are the carry flag, auxiliary carry flag, sign flag, parity flag, and zero flag, which provide essential information about the results of operations.

15:03

🔌 The Role of Timing and Control Unit and Interrupts

This paragraph discusses the timing and control unit's role in synchronizing the CPU's operations through clock signals and control signals. It explains how these signals manage the execution of the instruction cycle and the interaction with hardware devices. The concept of interrupts is introduced, describing them as signals that pause the CPU's current activity to respond to external events. The paragraph outlines different types of interrupts supported by the 8085, including software, hardware, vector, non-vector, maskable, and non-maskable interrupts. The importance of interrupts in managing real-time events and their classification is emphasized.

🛠️ Bus Architecture and the 8085 Microprocessor's Communication

The final paragraph concludes the tutorial by discussing the 8085's bus architecture and how the microprocessor communicates with system hardware components. It describes the address bus, data bus, and control bus, explaining their functions in transferring addresses, data, and control signals. The address bus transfers 16-bit addresses between the CPU and main memory, the data bus facilitates 8-bit data transfer, and the control bus manages signals to hardware devices. The paragraph provides a complete understanding of the 8085's communication infrastructure, wrapping up the tutorial on the microprocessor's architecture.

Keywords

💡Intel 8085 Microprocessor

The Intel 8085 microprocessor is an 8-bit CPU launched by Intel Corporation in 1976. It is one of the first and most commercially successful 8-bit processors, still used in many devices today. The video script focuses on the architecture of this microprocessor, which is foundational knowledge for understanding more complex microprocessor designs. The 8085's architecture is broken down into functional units, making it easier to grasp the basics of how a CPU operates.

💡Microprocessor Architecture

Microprocessor architecture refers to the design and layout of the functional components within a microprocessor chip and how they interact with each other during operations. The video provides an in-depth look at the 8085's architecture, which includes the memory unit, ALU, instruction decoder, timing and control unit, and interrupts and serial communication unit. This concept is central to the video's theme, as it forms the basis for understanding how the 8085 microprocessor functions.

💡Instruction Cycle

The instruction cycle is a fundamental operation of the CPU, involving a three-step process: fetch, decode, and execute. In the context of the video, the instruction cycle is how the CPU executes program instructions stored in memory. The script explains that the CPU initiates program execution by repetitively performing this cycle, which is essential for understanding the basic functioning of the 8085 microprocessor.

💡Arithmetic Logic Unit (ALU)

The ALU is a critical component of the processor responsible for performing arithmetic and logical operations on data. The video script describes the ALU as part of the 8085 microprocessor, where it operates on the data placed in the accumulator according to the operation code decoded by the control unit. The ALU's role is to carry out the actual data manipulations as directed by the program instructions.

💡General Purpose Registers

General purpose registers are used to store data temporarily during program execution. The 8085 microprocessor has six such registers (B, C, D, E, H, and L), which can also be combined to form register pairs for 16-bit operations. These registers are essential for the video's narrative as they are used by the 8085 to handle data during the execution of instructions.

💡Special Purpose Registers

Special purpose registers are used to store specific types of data and perform special functions. The video script mentions several special purpose registers in the 8085 architecture, such as the program counter (PC), instruction register (IR), and the accumulator, which are vital for the microprocessor's operation. These registers are used in specific contexts, like storing the address of the next instruction to be fetched or the part of the instruction to be decoded.

💡Flag Register

The flag register, also known as the program status word (PSW), is an 8-bit special purpose register that indicates the status of the processor after each ALU operation. The video script explains that the flag register contains flags like carry, auxiliary carry, sign, parity, and zero, which are crucial for conditional branching and other operations based on the result of the ALU operations.

💡Timing and Control Unit

The timing and control unit generates clock pulses and control signals that synchronize the operations of the CPU's internal components and external hardware devices. The video script describes this unit as essential for managing and controlling the operations of various hardware components during the instruction cycle, highlighting its importance in the overall functioning of the 8085 microprocessor.

💡Interrupts

Interrupts are signals that pause the current activity of the CPU to attend to a request from an external device. The video script explains that the 8085 supports eight software interrupts and five hardware interrupts, which can be classified into various types such as software, hardware, vector, non-vector, maskable, and non-maskable interrupts. Understanding interrupts is key to grasping how the 8085 handles external events and real-time requests.

💡Bus Architecture

Bus architecture involves the collection of wires through which data, addresses, and control signals are transferred within the computer system. The video script details the 8085's 8-bit data bus and 16-bit address bus, which are crucial for communication between the microprocessor and other system components. The bus architecture is fundamental to the video's explanation of how the 8085 microprocessor interfaces with the rest of the computer system.

Highlights

The 8085 microprocessor was one of the first 8-bit processors launched by Intel in 1976.

It was one of the most commercially successful processors and is still used in many devices.

Studying the 8085 architecture is fundamental for understanding more complex microprocessor architectures.

The microprocessor executes programs by fetching, decoding, and executing instructions in an instruction cycle.

Microprocessor architecture involves the design and layout of functional components and their interactions.

The 8085 microprocessor can be broken down into five major functional units for simplified study.

Technical features of the 8085 include an 8-bit processor with 40 pins, operating on a plus 5 volts supply.

It has variants with execution speeds of 3.5 and 6 megahertz and supports a 16-bit address bus.

The 8085 has a 16-bit program counter register and a 16-bit stack pointer for addressing memory.

It features 6 general-purpose 8-bit registers and can perform 16-bit operations by combining them into pairs.

The 8085 operates at 3.2 megahertz with a single-phase clock and supports multiple software and hardware interrupts.

The memory unit, also known as the register unit, is used for storing data, addresses, and machine instructions.

General-purpose registers are used for temporary data storage during program execution.

Special-purpose registers perform specific functions and some are accessible to programmers.

The program counter register (PC) stores the address of the next instruction to be fetched.

The instruction register (IR) holds the part of the instruction to be decoded.

The accumulator is part of the ALU and stores the operand for arithmetic and logical operations.

The flag register indicates the status of the processor after each ALU operation.

The timing and control unit generates clock pulses and control signals for synchronized operations.

Interrupts allow the microprocessor to pause current activity and respond to external events or peripheral device requests.

The 8085 supports eight software interrupts and five hardware interrupts, classified into various types.

The 8085 bus architecture includes an 8-bit data bus and a 16-bit address bus for data, address, and control signal transfer.

Transcripts

if you are looking for a complete guide

that will help you

understand the intel 808.5

microprocessor architecture

in the most simplified language then

this video tutorial is for you

in this video you will learn 808.5

architecture

its functional components and the

interaction between

various functional units step by step

let us start with a quick introduction

to 8085 microprocessor

the 8085 microprocessor was one of the

first 8-bit processor

launched by the intel corporation in

year 1976.

this was also one of the most

commercially successful processor

that is still being used in many devices

after the success of 808.5 processor the

intel

also launched many processors with

16-bit

32-bit and 64-bit architecture

however it is important for the students

of computer science

to first study the 808.5 architecture in

detail

this will help you understand some of

the most important

foundational concepts necessary to study

the microprocessor architecture

and how cpu works once you learn 808.5

architecture

then learning other complex architecture

will be much easier for you

welcome to learn computer

learncomputerscienceonline.com

and in this video we are going to

discuss intel 8085 microprocessor

architecture

in detail in this video you will learn

all the foundational concepts necessary

to understand

the intel 8085 microprocessor

architecture

its functional units and the technical

features

before we dive into our main topic it is

important to first understand

the functioning of the microprocessor

and how cpu works

the microprocessor is the brain of the

computer system

the main function of the microprocessor

is to execute the program

a computer program essentially consists

of

set of instructions that directs the cpu

to perform various operations as per the

program instruction

the program instructions are stored into

the main memory

ram each program instruction residing in

the memory

is a represented by machine instruction

in binary

these machine instruction in binary can

be directly decoded

and executed by the processor the cpu

initiates the program

execution by fetching decoding and

executing

each instruction one by one the cpu

executes the program

by repetitively performing its basic

operation

called the instruction cycle the

instruction cycle

is a three-step cpu operation which

includes

fetch decode and the execute operation

so now i presume you know how

microprocessor works

let us now move on to the next topic

since we are studying

the microprocessor architecture let us

find out

what is microprocessor architecture is

all about

the term microprocessor architecture is

the design

and the layout of various functional

components

that exist inside the microprocessor

chip

and how these various functional units

interact with each other

when the microprocessor performs various

operations

in order to simplify the study of 8085

architecture

let us group all the microprocessor

components

into five major functional units

each of these functional unit performs a

specific role

these microprocessor functional units

are as follows

the first unit as the memory unit it is

also referred to as

the register unit the second unit is the

arithmetic

and logic unit alu the third unit is the

instruction decoder and the machine

cycle encoder unit

the fourth unit is the timing and

control unit

and finally the fifth unit as the

interrupts

and the serial communication unit let us

now take

a quick look at some important technical

features of the

808.5 microprocessor it is a

8-bit processor and this processor has

total 40 pins it works on

plus 5 volts supply it has a execution

speed of

3 5 and 6 megahertz variants

are available it has 8-bit data bus

in other words it has 8-bit word length

it has 16-bit address bus

and it can address up to 64 kilobyte of

memory

it has a 16-bit program counter register

pc it also has a 16-bit

stack pointer it has 6 8-bit

general purpose registers referred by

its name

that is b c d e and

h l this processor operates at

3.2 megahertz single phase clock

the 8085 processor supports eight

software interrupts

and five hardware interrupts

let us now discuss each of the five 8085

microprocessor functional units

in detail let us start with the first

unit

that is memory unit also called as the

register unit

the internal memory of the processor

built into the processor chip

is called a register in other words

the cpu registers are high speed

temporary memory

present inside the processor chip these

registers are used by the 8085 processor

to store the data addresses and machine

instructions

during the program execution the cpu

makes use of

different types of registers placed

inside the processor chip

the cpu registers can be grouped into

two types the first type is called

general purpose registers and the second

type is called

the special purpose register the general

purpose registers are used

to store the data in the temporary

memory during the program

execution the 8085 processor has

six general purpose registers that can

store

eight bit of data the general purpose

registers

are named as b c d e

h and l these registers can also be

combined

to form a register pair such as bc

di and hl to perform the 16-bit

operations

the 8085 processor also make use of

some special purpose registers during

the execution of the

instruction cycle the special purpose

registers

are used to store a specific type of

data and perform

a special function and therefore they

are called as

special purpose registers some special

purpose registers

are accessible to the programmer whereas

some special purpose registers

are not accessible to the programmer let

us now take

a quick look at some important registers

and

their functions the first register that

comes into action

is the program counter register pc the

program counter register

is a 16-bit special purpose register

used in the 8085 architecture

to store the address of the instruction

that needs to be fetched

from the memory the program counter

register

always stores the memory address of the

next instruction

that needs to be fetched from the main

memory ram

as the processor begins the fetch

operation for the first instruction

the program counter register is

incremented by one

at the same time so that it now points

to the

address of the next instruction that is

to be fetched

from the memory the second register that

comes into action

is the instruction register ir

the instruction register is a 8-bit

special special-purpose register

used by the processor to store the part

of the instruction

that needs to be decoded by the decoder

of the control unit

depending upon the instruction format

the control unit of the cpu

decodes the instruction as specified in

the

op code of the instruction format

the opcode stands for operation code

it is opcode that is decoded by the

decoder

and machine instruction encoder unit the

opcode part of the instruction

is stored into the 8-bit instruction

register

during the execution of the instruction

cycle

the third register that comes into

action is the

accumulator register the accumulator is

considered to be

a part of arithmetic and logic unit alu

the accumulator stores the operand part

of the

instruction format the arithmetic and

logic unit alu

is another important component of the

processor which actually performs

the arithmetic and logical operations

the arithmetic and logic unit of the cpu

performs the desired operation on the

data

placed in the accumulator as per the

operation code

decoded by the decoder of the control

unit

let us now understand what is flag

register

as we have discussed earlier all

arithmetic and logical operations are

performed by the alu

during the alu operations the flag

register plays an important role

the main function of the flag register

is to indicate

the status of the processor after each

alu

operation the flag register is also

alternately referred to as

program status word psw of flag register

is a 8-bit special purpose register used

in 808.5 architecture

to indicate the cpu status after each

arithmetic

and logical operation the 8085 flags

register

can have a total of eight flags each

flag

is represented by a specific bit in the

8-bit

flag register however the 8085

processor use only five flags out of

eight flags

and the remaining three flags are kept

unused

the five flags used in the flag register

include

the carry flag auxiliary carry flag

sign flag parity flag and the zero flag

all right so far we have discussed in

detail

different types of cpu registers and

their respective functions

let us now move on to next important

topic

and that topic is timing and control

unit of the

8085 microprocessor the cpu is driven by

a stream of the clock signals generated

by the

clock circuit built into the processor

chip

these clock signals helps the cpu to

synchronize the operations of

its internal components various

registers

and other external hardware devices

the clock pulses and the control signals

are generated

by the timing and control unit of the

cpu that is built into the processor

chip

the control signals are essential to

manage and control

the operations of the various hardware

devices

connected to the system the control unit

of the

processor also sends the control signals

to all the hardware components and

peripheral devices

necessary to control their operations

the timing and control signals are

essential part of the

instruction cycle which is a basic

operation of the cpu

the cpu to execute the program

instructions

one by one by repetitively performing

the instruction cycle

for each clock pulse the cpu executes

a part of the instruction during the

program execution

okay so now you know the importance of

timing and control unit of the cpu

let us now discuss another important

component of the 8085 architecture

and that topic is interrupts as the name

suggests

the interrupts are used to current

execution sequence of the cpu

the interrupts are the signals sent to

the microprocessor

to pause the current activity and attend

to the request

sent by the external devices in other

words

the interrupts are external events that

occur in real time

to seek the processor response the

interrupts can be generated

either by the program instructions or it

can also be generated by the peripheral

devices

connected to the system the

architecture supports eight software

interrupts

and five hardware interrupts the

interrupt can be classified into the

following groups depending upon their

parameters

the interrupt types are first the

software interrupt

second the hardware interrupt third

vector interrupt

fourth non-vector interrupt fifth

maskable interrupt and finally sixth the

non-maskable interrupt all right

so far we have discussed what are

interrupts

and different types of interrupts used

in the

8085 processor

let us now discuss the final topic of

this video tutorial

which is another important component of

the 8085 architecture

and that topic is 808.5 bus architecture

and the bus interface the computer buses

are

the group of wires running across the

computer system

through which the data address and the

control signals are transferred

the microprocessor needs to communicate

with the

various system hardware components in

order to execute

the program instructions the

microprocessor chip

also has its own internal buses

essential for the

functioning of the processor the 8085

architecture has

8-bit data bus and 16-bit

address bus let us now discuss

different types of buses and its

function

the first component of the bus

architecture is the address bus

the address bus is a 16-bit

unidirectional bus

that is used to transfer the 16-bit

address

between the cpu and the main memory ram

the second component of the bus

architecture is the data bus

the data bus is a 8-bit bi-directional

bus

that is used to transfer the 8-bit data

between the cpu

and the main memory ram the cpu performs

both memory read and write operation

during the program

execution this data transfer takes place

on the data bus the third component of

the

bus architecture is the control bus

the control bus is a bidirectional bus

that is used to transfer

the control signals between the cpu and

the various hardware devices connected

to the computer system

all right so now you have enough

knowledge about

all important cpu components various

functional units

and the technical features for intel

8085

microprocessor architecture

and that brings us to the end of this

tutorial

please read the detailed article on our

website

learncomputerscienceonline.com for more

details

and in this tutorial we have discussed

the intel 8085 architecture in detail

if you have liked this video then please

give us a thumbs up

and do consider to subscribe to this

channel

for more such interesting videos thanks

for watching

and i will see you soon with another

computer science video tutorial