Unit Five: Introduction to Microprocessor and Its Components

Definition of Microprocessor

A Microprocessor is a programmable electronic device that works as the Central Processing Unit (CPU) of a computer system or other digital electronic device.

According to the provided notes, it integrates functions such as:

Central Processing Unit (CPU)
Memory Management Unit (MMU)
Input/Output (I/O) interfaces

on a single Integrated Circuit (IC) chip.

General Terms

Bit

A Bit is a binary digit.

It can have either of two values:

0 or 1

Byte

A Byte is a group of:

8 bits

Nibble

A Nibble is a group of:

4 bits

Word

A Word is a group of bits used for a particular purpose.

For example, a 4-bit computer may have a word consisting of 4 bits.

Instruction

An Instruction is a command in binary form that is recognized and executed by a computer to perform a particular task.

Program

A Program is a set of instructions arranged in sequence to accomplish a given task.

Machine Language

Machine Language is a binary medium of communication used by a computer.

Low-Level Language

A Low-Level Language is machine-dependent and is specific to a particular computer system.

Examples include:

Machine Language
Assembly Language

Programs written in such languages are generally not directly transferable between different types of machines.

High-Level Language

A High-Level Language is largely independent of the computer hardware.

Programs are written using English-like statements and require a translator for execution.

Compiler

A Compiler is a program that translates a high-level language program into low-level or machine language.

The translated machine-language program is called Object Code.

Interpreter

An Interpreter translates high-level language statements into machine language one statement at a time.

Process

A Process is a series of actions or steps performed to achieve a particular result.

Processor

A Processor is a device or machine that performs processing operations.

Integrated Circuit (IC)

An IC combines multiple electronic circuit functions into a single chip.

Microprocessor

When the:

Arithmetic and Logic Unit (ALU)
Control Unit (CU)
Registers

are integrated into a single chip using LSI or VLSI technology, the resulting processor is called a Microprocessor Unit (MPU) or simply a Microprocessor.

According to the notes, a microprocessor:

Is a multipurpose programmable electronic device.
Reads binary instructions from storage.
Accepts binary data as input.
Processes data according to instructions.
Produces output.
Operates using binary digits 0 and 1.
Has a fixed set of machine-language instructions.
Commonly serves as the CPU of a computer system.

Applications of Microprocessor

Microprocessors can be used in many different areas.

The notes discuss the following applications:

Test Instruments
Communication
Computers
Industries

1. Test Instruments

Microprocessors are used in instruments such as:

Signal generators
Oscilloscopes
Counters
Digital multimeters
X-ray analyzers
Blood group analyzers
Baby incubators
Frequency synthesizers
Data acquisition systems
Spectrum analyzers

According to the notes, the Fluke 6010A synthesized signal generator uses the 4004 microprocessor.

2. Communication

Modern communication systems require a large number of circuits to be managed.

Microprocessors can be used to:

Receive data
Check errors
Analyze information
Make decisions quickly
Perform computational tasks

3. Computer

The microprocessor acts as the Central Processing Unit of a microcomputer.

It performs:

Arithmetic operations
Logical operations
Control operations

The Control Unit sends control signals to:

Input units
Output units
Memory
ALU

and manages the sequence of operations.

4. Industries

Microprocessors are used in industrial applications such as:

Data monitoring systems
Smart cameras for quality control
Automatic weighing systems
Batching systems
Assembly-machine control

Basic Characteristics of a Microprocessor

Important characteristics include:

Instruction Set

The Instruction Set is the total number of instructions that a microprocessor can execute.

Bandwidth

Bandwidth refers to the number of bits processed in a single operation or system.

Examples given in the notes include:

32-bit
64-bit

Clock Speed

According to the notes, Clock Speed represents the number of instructions that a processor can execute per second.

The notes mention MIPS – Millions of Instructions Per Second.

Basic Block Diagram of a Computer

A basic computer system consists of several important components that work together to process data.

The major components are:

Input Unit
Output Unit
Memory
Central Processing Unit

Input Unit

The Input Unit allows users to enter data and instructions into a computer.

Examples include:

Keyboard
Mouse
Touchscreen
Microphone

Output Unit

The Output Unit provides processed information to the user.

Examples include:

Monitor
Printer
Speaker
Headphones

Memory

Memory is used to store data and instructions.

The notes mention:

RAM
Hard Disk Drive
Solid-State Drive

RAM temporarily stores data and instructions required by the CPU.

Other storage devices provide long-term storage.

Central Processing Unit (CPU)

The CPU contains important internal components.

These include:

Control Unit
Arithmetic Logic Unit
Registers

1. Control Unit

The Control Unit (CU) controls the execution of instructions.

It:

Decodes instructions
Controls data flow
Coordinates CPU components
Coordinates communication with other parts of the system

2. Arithmetic Logic Unit

The Arithmetic Logic Unit (ALU) performs arithmetic and logical operations.

Examples include:

Addition
Subtraction
AND
OR

3. Registers

Registers are small, high-speed storage locations inside the CPU.

They temporarily store:

Data
Intermediate results
Memory addresses

Examples include:

Program Counter
Instruction Register
General-Purpose Registers

8085 Bus Structure and Internal Architecture

The 8085 microprocessor system uses three major buses:

Address Bus
Data Bus
Control Bus

Data transfer between different units takes place through the system bus.

Microprocessor Unit

The main units of the microprocessor include:

ALU
Control Unit
Register Unit

ALU

The ALU:

Performs arithmetic operations.
Performs logical operations.
Handles operations such as addition, subtraction, AND, OR, and XOR.

Control Unit

The Control Unit:

Manages execution of instructions.
Controls data flow inside the CPU.
Controls communication between the CPU and other system components.

Register Unit

The Register Unit consists of different registers.

Registers provide temporary storage during program execution and can be accessed using instructions.

Memory

Memory stores binary information such as:

Instructions
Data

The microprocessor reads instructions and data from memory during program execution.

According to the notes:

ROM stores programs and data that generally do not need modification.
RAM stores programs and data that can be rewritten or modified according to requirements.

System Bus

The System Bus provides a communication path between the microprocessor and peripheral devices.

It carries:

Data
Addresses
Control signals

The system bus contains:

Data Bus
Address Bus
Control Bus

I/O Bus

The Input/Output bus is used for communication between the microprocessor and external devices.

Input Unit supplies data or instructions to the microprocessor.
Output Unit carries processed information from the microprocessor.

Bus Organization

1. Address Bus

The Address Bus is generally unidirectional.

According to the notes, it may contain:

parallel lines.

The microprocessor sends the address of a memory location or I/O device through the address bus.

The number of address-bus bits determines the maximum number of memory locations that can be addressed.

Formula:

Number of Memory Locations = 2^(Number of Address Bus Bits)

For a 16-bit address bus:

2¹⁶ = 65,536

2. Data Bus

The Data Bus is bidirectional.

According to the notes, it can consist of:

parallel lines.

It carries data between:

Microprocessor
Memory
Peripheral devices

The width of the data bus affects the amount of data transferred at a time.

If an 8-bit data bus has to transfer 16-bit data, it generally requires two cycles.

3. Control Bus

The Control Bus carries control and timing signals.

According to the notes, it may contain around 4 to 10 parallel lines.

Its functions include:

Controlling access to the address bus
Controlling access to the data bus
Sending command signals
Sending timing signals

Examples include:

Memory Read
Memory Write
I/O Read
I/O Write
Bus Request
Bus Grant

Stored Program Concept and Von Neumann Machine

The Stored Program Concept and Von Neumann Architecture are important principles in computer organization.

1. Stored Program Concept

The Stored Program Concept states that:

Instructions
Data

can both be stored in the same memory.

According to the notes, this concept allows programs to be stored, modified, and executed along with data.

The concept is associated with John von Neumann.

2. Von Neumann Machine

A Von Neumann Machine is a computing model based on the Stored Program Concept.

The notes describe four major components:

CPU
Memory
Input/Output
Control Unit

Central Processing Unit

The CPU executes instructions stored in memory.

It contains:

ALU
Control Unit

Memory

Memory stores both:

Data
Instructions

The information is stored in binary form.

Input/Output

Input/Output components provide communication between the computer and the external environment.

Control Unit

The Control Unit:

Fetches instructions from memory
Decodes instructions
Controls their execution

In a Von Neumann machine, instructions and data share the same memory space.

8085 Microprocessor Architecture and Operations

Figure: Add Functional Block Diagram of 8085 Microprocessor here.

The major components of the 8085 architecture discussed in the notes include:

ALU
Timing and Control Unit
Instruction Register and Decoder
Register Array
System Bus
Interrupt Control
Serial I/O Control

1. ALU

The ALU performs numerical and logical operations such as:

Addition
Subtraction
AND
OR

According to the notes, it uses data from memory and the accumulator and generally stores the result in the accumulator.

The ALU includes:

Accumulator
Flag Register
Temporary Register

Accumulator

The Accumulator is used during:

Input/Output operations
Arithmetic operations
Logical operations

It is directly connected to:

ALU
Internal data bus

According to the notes, many arithmetic and logical operation results are stored in the accumulator.

Flag Register

The Flag Register is an 8-bit register used to indicate the status of arithmetic and logical operations.

The 8085 uses the following important flags:

Sign Flag
Zero Flag
Auxiliary Carry Flag
Parity Flag
Carry Flag

1. Sign Flag

The Sign Flag (S) indicates the sign of the result.

If the Most Significant Bit is set, the sign flag is set.

2. Zero Flag

The Zero Flag (Z) is set when the result of an operation is zero.

3. Auxiliary Carry Flag

The Auxiliary Carry Flag (AC) is used in BCD arithmetic.

It is set when a carry occurs from the lower nibble to the upper nibble.

4. Parity Flag

The Parity Flag (P) indicates whether the number of 1 bits in the result is even or odd.

According to the notes, it is set when the number of set bits is even.

5. Carry Flag

The Carry Flag (CY) is set when a carry occurs from the Most Significant Bit during operations such as:

Addition
Subtraction
Comparison

It is also used in certain rotate operations.

2. Timing and Control Unit

The Timing and Control Unit produces timing and control signals required for microprocessor operations.

It:

Synchronizes operations with the clock.
Generates control signals.
Controls communication with peripheral devices.

3. Instruction Register and Decoder

When an instruction is fetched from memory, it is loaded into the Instruction Register.

The Instruction Decoder interprets the instruction and determines the sequence of operations required.

According to the notes, the Instruction Register cannot be directly accessed through ordinary instructions.

4. Register Array

The 8085 contains several registers.

General-Purpose Registers

The six general-purpose registers are:

They are 8-bit registers.

They can also be used in pairs:

for some 16-bit operations.

W and Z Registers

The internal registers W and Z temporarily hold 8-bit data during execution of some instructions.

Stack Pointer

The Stack Pointer (SP) is a 16-bit register.

It points to the address of the top of the stack.

Program Counter

The Program Counter (PC) is a 16-bit register.

It points to the address of the next instruction to be fetched and executed.

5. System Bus

The system bus includes:

Data Bus

Carries binary data between the microprocessor and external units such as memory.

Address Bus

Carries the address of the operand or memory location.

Control Bus

Carries control signals used to coordinate operations.

Examples include:

Read
Write

6. Interrupt Control

An Interrupt is a signal that temporarily suspends the current microprocessor operation and transfers control to another routine.

After the interrupt service routine completes, control returns to the main program.

Interrupts may be:

Hardware interrupts
Software interrupts
Maskable interrupts
Non-maskable interrupts

The notes mention:

INTR
TRAP
RST 7.5
RST 6.5
RST 5.5

7. Serial I/O Control

The 8085 supports serial data transmission one bit at a time.

It uses two signals:

SID – Serial Input Data
SOD – Serial Output Data

Intel 8085 Microprocessor

Figure: Add 8085 Microprocessor Pin Diagram here.

According to the provided notes, the Intel 8085:

Is an 8-bit microprocessor.
Uses NMOS technology.
Has a 16-bit address bus.
Can address up to 2¹⁶ = 65,536 bytes.
Multiplexes the lower 8 address lines with the data bus.
Has a 16-bit Program Counter.
Has a 16-bit Stack Pointer.
Has six 8-bit general-purpose registers.
Requires a +5V power supply.
Uses a 40-pin package.

Address Bus in 8085

The 8085 uses 16 address lines.

The address bus is divided into:

A15 to A8
AD7 to AD0

A15 to A8 carry the higher-order address.

AD7 to AD0 are multiplexed and perform more than one function.

Data Bus

According to the notes, the lower-order address/data lines are associated with pins 12–19.

AD0–AD7 can be used as:

Lower-order address bus
Data bus

The ALE signal is used to distinguish the address from data.

Control and Status Signals

The control and status signals help identify the type of operation being performed.

Read Control Signal

RD̅

This is an active-low read control signal.

It indicates that the selected:

Memory device
I/O device

is to be read.

Write Control Signal

WR̅

This is an active-low write control signal.

It indicates that the selected:

Memory device
I/O device

is to be written to.

Status Signals

The notes mention three important status signals:

IO/M̅
S1
S0

Status Signal Table

IO/M̅	S1	S0	Operation
0	1	1	Opcode Fetch
0	1	0	Memory Read
1	1	0	I/O Read
0	0	1	Memory Write
1	0	1	I/O Write
—	0	0	No Operation

ALE

According to the notes:

When:

ALE = 1

AD0–AD7 act as an Address Bus.

When:

ALE = 0

AD0–AD7 act as a Data Bus.

Power Supply and Frequency Signals

The notes mention:

+5V DC on pin 40
Ground on pin 20
X1 and X2 for oscillator connection
Crystal oscillator connection on pins 1 and 2

CLK OUT

The CLK OUT signal is available on pin 37.

It can be used as a system clock for other devices.

Externally Initiated Signals

INTR

INTR is an interrupt-request input.

It is used as a general-purpose interrupt.

INTA̅

INTA̅ is the Interrupt Acknowledge output.

It acknowledges an interrupt request.

RST 7.5, RST 6.5 and RST 5.5

These are restart interrupts.

According to the notes:

They are vectored interrupts.
They transfer program control to specific memory locations.
They have higher priority than INTR.

Registers in Intel 8085

The notes list the following registers:

Accumulator A – 8-bit
BC, DE, HL – General-purpose register pairs
PC – 16-bit
SP – 16-bit
W and Z – Temporary 8-bit registers
Instruction Register – 8-bit system register

Additional Externally Initiated Signals

TRAP

TRAP is a non-maskable interrupt.

According to the notes, it has high priority.

HOLD

HOLD indicates that a peripheral device such as a DMA controller is requesting control of the system bus.

HLDA

HLDA acknowledges a HOLD request.

READY

The READY signal is used when slower peripheral devices require additional time before completing a read or write operation.

RESET IN

When the RESET IN signal becomes active, the microprocessor is reset.

According to the notes, the Program Counter is set to 0.

RESET OUT

RESET OUT indicates that the microprocessor is being reset.

It can also be used to reset other system devices.

Serial I/O Ports

The 8085 contains two pins for serial communication:

SOD – Serial Output Data
SID – Serial Input Data

According to the notes:

SOD is pin 4.
SID is pin 5.

Serial data is transmitted one bit at a time through a single communication line.

Instruction

An Instruction is a command given to the microprocessor to perform a specific task on specified data.

Each instruction has two main components:

Opcode
Operand

Opcode

The Opcode specifies the operation to be performed.

Operand

The Operand is the data on which the operation is performed.

Example

ADD B

Here:

ADD = Opcode
B = Operand

Therefore, the complete instruction contains both the opcode and operand.

Addressing Modes

An instruction performs an operation on specified data.

The operand may be located in:

General-purpose register
Accumulator
Memory location
Instruction itself

The method used to specify the operand is called an Addressing Mode.

The notes discuss:

Implied Addressing
Immediate Addressing
Register Addressing
Direct Addressing
Register Indirect Addressing

1. Implied or Implicit Addressing

In Implied Addressing Mode, the instruction does not explicitly specify an operand.

Examples:

Where:

EI = Enable Interrupt
STC = Set Carry Flag
NOP = No Operation

2. Immediate Addressing

In Immediate Addressing Mode, the operand is directly included in the instruction.

The operand may be:

8-bit data
16-bit data

Examples:

MVI B, 05H

LXI B, 7A21H

ADI 72H

3. Register Addressing

In Register Addressing Mode, a register contains the operand.

Examples:

MOV A, B

ADD B

4. Direct Addressing

In Direct Addressing Mode, the address of the operand is directly specified in the instruction.

Examples:

LDA 2035H

STA 2500H

IN 07H

According to the provided notes:

LDA 2035H means the accumulator receives the data stored at memory address 2035H.

STA 2500H stores accumulator data at address 2500H.

5. Register Indirect Addressing

In Register Indirect Addressing Mode, the address of the operand is stored in a register pair.

Examples:

LDAX B

If:

B = 23H
C = 50H

then BC points to address:

2350H

STAX D

If:

D = 30H
E = 10H

then DE points to:

3010H

Another example is:

MOV A, M

where M refers to the memory location whose address is stored in HL.

Instruction and Data Flow

An instruction is a binary pattern designed to perform a particular function.

The complete set of instructions supported by a microprocessor is called the Instruction Set.

The instruction set determines the operations a microprocessor can perform.

Notations Used

According to the notes:

R = 8085 8-bit register such as B, C, D, E, H, L
M = Memory location pointed to by HL
Rs = Source Register
Rd = Destination Register
Rp = Register Pair such as BC, DE, HL
( ) = Contents of a register or memory location

Data Transfer Instructions

Data Transfer Instructions are used to copy or move data.

They perform operations such as:

Loading 8-bit data into a register.
Loading 16-bit data into a register pair.
Copying data from one register to another.
Copying data between registers and memory.
Copying data between I/O ports and accumulator.
Copying data between registers and stack memory.

Important Data Transfer Instructions

Instruction	Function
MVI R, 8-bit	Loads 8-bit immediate data into a register
MOV Rd, Rs	Copies data from source register to destination register
LXI Rp, 16-bit	Loads 16-bit data into a register pair
OUT 8-bit	Writes data to an output port
IN 8-bit	Reads data from an input port
LDA 16-bit	Loads accumulator from a specified memory address
STA 16-bit	Stores accumulator contents at a specified memory address
LDAX Rp	Loads accumulator from memory addressed by a register pair
STAX Rp	Stores accumulator data in memory addressed by a register pair
MOV R, M	Copies memory content into a register
MOV M, R	Copies register content into memory

Arithmetic Instructions

Arithmetic instructions perform operations such as:

Addition
Subtraction
Increment
Decrement

Important Arithmetic Instructions

Instruction	Function
ADD R	Adds register contents to the accumulator
ADI 8-bit	Adds immediate 8-bit data to the accumulator
ADD M	Adds memory contents to the accumulator
SUB R	Subtracts register contents from the accumulator
SUI 8-bit	Subtracts immediate 8-bit data from the accumulator
SUB M	Subtracts memory contents from the accumulator
INR R	Increments register contents by 1
INR M	Increments memory contents by 1
DCR R	Decrements register contents by 1
DCR M	Decrements memory contents by 1
INX Rp	Increments a register pair by 1
DCX Rp	Decrements a register pair by 1

Logical and Bit Manipulation Instructions

These instructions include operations such as:

AND
OR
XOR
Compare
Rotate bits

Important Logical Instructions

ANA R

Performs logical AND between a register and the accumulator.

ANI 8-bit

Performs logical AND between immediate 8-bit data and the accumulator.

ANA M

Performs logical AND between memory contents and the accumulator.

ORA R

Performs logical OR operation involving a register.

ORI 8-bit

The source lists this as an immediate OR instruction but does not provide additional explanation.

ORA M

The source lists this instruction without further explanation.

XRA R

Performs logical Exclusive-OR between a register and the accumulator.

XRI 8-bit

The source lists this as an immediate XOR instruction without further explanation.

XRA M

The source lists this instruction without further explanation.

CMP R

Compares register contents with accumulator contents.

CPI 8-bit

Compares immediate 8-bit data with the accumulator.

Branching Instructions

Branching instructions change the normal sequence of program execution.

The notes list:

JMP 16-bit

Jumps unconditionally to a specified 16-bit address.

JZ 16-bit

Jumps to the specified address if the Zero Flag is set.

JNZ 16-bit

Jumps to the specified address if the Zero Flag is reset.

JC 16-bit

Jumps to the specified address if the Carry Flag is set.

JNC 16-bit

The source lists this instruction but does not provide its description.

CALL 16-bit

The source lists this instruction but does not provide its description.

RET

The source lists the RET instruction without further explanation.