Topic 1: Basics of Microprocessor (8 Marks)

Basics of Microprocessor

The microprocessor is sometimes referred to as the 'brain' of the personal computer, and is

responsible for the processing of the instructions which make up computer software. It

houses the central processing unit, commonly referred to as the CPU, and as such is a

crucially important part of the home PC. However, how many people really understand how

the chip itself works?

CPU Structure

This section, using a simplified model of a central processing unit as an example, takes you

through the role of each of the major constituent parts of the CPU. It also looks more

closely at each part, and examines how they are constructed and how they perform their role within the microprocessor.

Instruction Execution

Once you are familiar with the various elements of the processor, this section looks at how

they work together to process and execute a program. It looks at how the various

instructions that form the program are recognised, together with the processes and actions that are carried out during the instruction execution cycle itself.

Further Features

Now that the basics have been covered, this section explores the further advancements in

the field of microprocessor architecture that have occured in recent years. Explanations of

such techniques as pipelining and hyperthreading are provided, together with a look at cache memory and trends in CPU architecture.

It is important that a computer remembers what it is doing and the data from inputs such as

sensors or the keyboard. Memory is used for this function.

Each piece of data (Byte) is placed in an „ADDRESS‟ in the memory and when the processor

needs to use the data it „fetches‟ it from its address. Another name for

the ADDRESS is LOCATION.

It is important to understand the way data is transmitted from one part of the computer

to another. Data is usually stored in the memory. Numbers, words or characters (data) is

stored as „BITs‟. These are “1‟s” and “0‟s”. These bits are arranged into „BYTES‟ - a

line of 1‟s and 0‟s.

This eight BIT BYTE could represent a letter from the alphabet or be a simple

instruction the computer has to carry out. Computers do not understand words or

sentences; in order to understand them the computer converts words into BITs and

BYTEs and then it can use them. The example is an eight bit BYTE, what do you think

a sixteen bit byte actually looks like? Each byte is placed in an address or location in

memory.

8085 Architecture

Introduction

As discussed earlier, 8085 microprocessor was introduced by Intel in the year 1976. This microprocessor is an update of 8080

microprocessor. The 8080 processor was updated with Enable/Disable instruction pins and Interrupt pins to form the 8085

microprocessor. Let us discuss the architecture of 8085 microprocessor in detail.

Features of 8085 microprocessor

Before knowing about the 8085 architecture in detail, lets us briefly discuss about the basic features of 8085 processor.

8085 microprocessor is an 8-bit microprocessor with a 40 pin dual in line package. The address and data bus are multiplexed in

this processor which helps in providing more control signals. 8085 microprocessor has 1 Non-maskable interrupt and 3 maskable

interrupts. It provides serial interfacing with serial input data (SID) and serial output data (SOD).

It has a set of registers for performing various operations. The various registers include

· Accumulator (register A)

· Registers: B, C, D, E, H and L

· Stack pointer

· Program Counter

· Temporary register

· Instruction register

Architecture of 8085 microprocessor

8085 consists of various units and each unit performs its own functions. The various units of a microprocessor are listed below

· Accumulator

· Arithmetic and logic Unit

· General purpose register

· Program counter

· Stack pointer

· Temporary register

· Flags

· Instruction register and Decoder

· Timing and Control unit

· Interrupt control

· Serial Input/output control

· Address buffer and Address-Data buffer

· Address bus and Data bus

Control Unit Generates signals within uP to carry out the instruction, which has been decoded. In reality causes certain connections between blocks of the uP to be opened or closed, so that data goes where it is required, and so that ALU operations occur. Arithmetic Logic Unit The ALU performs the actual numerical and logic operation such as ‘add’, ‘subtract’, ‘AND’, ‘OR’, etc. Uses data from memory and from Accumulator to perform arithmetic. Always stores result of operation in Accumulator.

Registers

Intel 8085 registers

15

14

13

12

11

10

09

08

07

06

05

04

03

02

01

00 (bit position)

Main registers

A Flags AF (accumulator and flags)

B C BC

D E DE

H L HL (indirect address)

Index registers

SP Stack Pointer

Program counter

PC Program Counter

Status register

S Z I H - P - C Flags

A register is a collection of eight D-type flip-flops with parallel-in and parallel-out operation.

A flip-flop can only store one bit at a time. Therefore to handle eight bits at a time , eight

flip-flops are required hence the term 8-bit register .Though the registers are all storage

areas inside the microprocessor . They differ in the purpose of storage data .Registers are

classified as :

General Purpose Registers

Special Purpose Registers

Temporary Registers

General Purpose Registers

The general purpose registers are used to store only the input data that is being used by

the program under execution .These general purpose registers are user accessible through

programs .Registers B,C,D,E,H and L are the general purpose registers in the 8085. The

General purpose registers are all 8-bit registers but they can handled as 16-bit registers as

well. This can be achieved by combining the register as pair B and C, D and E and H and L

to perform 16 bit operations. They are named as register pair BC, DE and HL.

Among theses pairs , HL has a special significance. A few memory related instruction of

8085 use the HL pair as memory pointer. The HP pair is pre-loaded with the memory

address in which data is available.

Special Purpose Registers

There are also special purpose registers that are dedicated to specific function.These are

given below:

Accumulator

Flag Registers Instruction Register

Accumulator

The accumulator is an 8-bit register; it is part of the Arithmetic and Logical Unit and is the

most important register of 8085 microprocessor.It is used to store 8-bit data and to perform

arithmetic and logical unit operations. The output of an operation is also stored in

accumulator. The accumulator is denoted as Register A . The programmer can use it at any

time to store 8-bit binary number. Being only eight bits long,it can hold only one byte at

time. Any previous data stored in this register will be overwritten as soon as new data is

stored. The 8085 Microprocessor communicates with input/output devices only through the

accumulator.

Flags The ALU includes five flip-flops, which are set or reset after an operation according to data conditions of the result in the accumulator and other registers. They are called Zero(Z), Carry (CY), Sign (S), Parity (P), and Auxiliary Carry (AC) flags; they are listed in the Table and their bit positions in the flag register are shown in the Figure below. The most commonly used flags are Zero, Carry, and Sign. The microprocessor uses these flags to test data conditions.

For example, after an addition of two numbers, if the sum in the accumulator id larger than eight bits, the flip-flop uses to indicate a carry -- called the Carry flag (CY) -- is set to one. When an arithmetic operation results in zero, the flip-flop called the Zero(Z) flag is set to one. The first Figure shows an 8-bit register, called the flag register, adjacent to the accumulator. However, it is not used as a register; five bit positions out of eight are used to store the outputs of the five flip-flops. The flags are stored in the 8-bit register so that the programmer can examine these flags (data conditions) by accessing the register through an instruction.

These flags have critical importance in the decision-making process of the microprocessor. The conditions (set or reset) of the flags are tested through the software instructions. For example, the instruction JC (Jump on Carry) is implemented to change the sequence of a program when CY flag is set. The thorough understanding of flag is essential in writing assembly language programs. Program Counter (PC) This 16-bit register deals with sequencing the execution of instructions. This register is a memory pointer. Memory locations have 16-bit addresses, and that is why this is a 16-bit register. The microprocessor uses this register to sequence the execution of the instructions. The function of the program counter is to point to the memory address from which the next byte is to be fetched. When a

byte (machine code) is being fetched, the program counter is incremented by one to point to the next memory location

Stack Pointer (SP) The stack pointer is also a 16-bit register used as a memory pointer. It points to a memory location in R/W memory, called the stack. The beginning of the stack is defined by loading 16-bit address in the stack pointer. The stack concept is explained in the chapter "Stack and Subroutines."

Instruction Register/Decoder Temporary store for the current instruction of a program. Latest instruction sent here from memory prior to execution. Decoder then takes instruction and ‘decodes’ or interprets the instruction. Decoded instruction then passed to next stage. Memory Address Register Holds address, received from PC, of next program instruction. Feeds the address bus with addresses of location of the program under execution. Control Generator Generates signals within uP to carry out the instruction which has been decoded. In reality causes certain connections between blocks of the uP to be opened or closed, so that data goes where it is required, and so that ALU operations occur. Register Selector This block controls the use of the register stack in the example. Just a logic circuit which switches between different registers in the set will receive instructions from Control Unit. General Purpose Registers uP requires extra registers for versatility. Can be used to store additional data during a program. More complex processors may have a variety of differently named registers. Microprogramming How does the µP knows what an instruction means, especially when it is only a binary number? The microprogram in a uP/uC is written by the chip designer and tells the uP/uC the meaning of each instruction uP/uC can then carry out operation.

Temporary Registers

Temporary registers are given below as :

Temporary Data Register

The ALU has two inputs. One input is supplied by the accumulator and other from temporary

data register. The programmer can not access this temporary data register. However it is

internally used for execution of most of the arithmetic and logical operations.

For example ADD B is the instruction which adds the content of register A and B and stores

the result in Accumulator. The addition operation is performed by ALU. The ALU takes input

from register A and temporary data register. The content of register B transferred to

temporary data register for applying second input to the ALU.

W and Z registers

W and Z registers are temporary registers . Theses registers are used to hold data during

execution of some instructions. These registers are not available for programmer,since 8085

uses them internally.

The CALL instruction is used to transfer program control to a sub program or subroutine.

This instruction pushes the content PC contents on to the stack and loads the given address

into the PC. The given address is temporarily stored in W and Z registers and placed on the

bus for the fetch cycle.Thus the program control is transferred to the address given in the

instruction . XCHG instruction exchanges the contents of H with D and L with E. At the time

of exchange W and Z registers are used for temporary storage of data.

Arithmetic and Logical Unit

ALU is the circuitry that performs the actual numerical and logical operations. Addition

(ADD), subtraction (SUB), increment (INR) ,decrement (DCR) and comparison (CMP) are

the arithmetic operations possible in 8085 microprocessor. The possible logical operations

are AND (AND), OR (OR), exclusive OR, complement (CMA) etc.

The ALU of the 8085 processor is called accumulator-oriented ALU . As one of the data used

in arithmetic and logic operations must be stored in the accumulator.The other data is

taken from an memory location or register. The results of the arithmetic and logical

operations are stored in accumulator. If the operation needs only one data,that data must

be stored in the accumulator.

Instruction Decoder

It is an 8- bit register that usually temporarily stores the instruction drawn from memory

locations before their actual execution. The content of the register is decoded by the

decoder circuitry,where the nature of the operation to be performed is decided . In addition,

there are two temporary registers W an Z , which are controlled internally and not available

for user access.

Address Buffer

This is an 8-bit unidirectional buffer. It is used to drive external high order address bus. It

is also used to tri-sate the high order address bus under certain conditions such as

reset,hold,halt and when address lines are not in use.

Address/Data Buffer

This is an 8-bit bi-directional buffer. It is used to drive multiplexed address/data bus (low

order address and data bus). It is also tri-state the multiplexed address/data bus under

certain conditions such as reset ,hold,halt and when the bus is not in use.

The address and data buffers are used to drive external address and data buses

respectively. Due to these buffers the address and data buses can be tri-stated when they

are not in use.

Increment/Decrement Address Latch

This 16-bit register is used to increment of decrements the contents of program counter or

stack pointer as a part of execution of instruction related to them.

Draw a neat labeled functional block diagram of 8085. State the function of

ALU. (Diagram : 3Marks; Any one function 1Mark)

8085 Pin Diagram

8085 is a 40 pin IC, The signals from the pins can be grouped as follows

1. Power supply and clock signals

2. Address bus

3. Data bus

4. Control and status signals

5. Interrupts and externally initiated signals

6. Serial I/O ports

1. Power supply and Clock frequency signals:

Vcc: + 5 volt power supply

Vss: Ground

X1, X2 : Crystal or R/C network or LC network connections to set the frequency of internal clock

generator. The frequency is internally divided by two. Since the basic operating timing frequency is 3

MHz, a 6 MHz crystal is connected externally. CLK (output)-Clock Output is used as the system clock

for peripheral and devices interfaced with the microprocessor.

2. Address Bus:

A8 - A15: (output; 3-state)

It carries the most significant 8 bits of the memory address or the 8 bits of the I/O address.

3. Data bus:

AD0 - AD7 (input/output; 3-state)

These multiplexed set of lines used to carry the lower order 8 bit address as well as data bus.

During the opcode fetch operation, in the first clock cycle, the lines deliver the lower order

address A0 - A7.

In the subsequent IO / memory, read / write clock cycle the lines are used as data bus.

The CPU may read or write out data through these lines.

4. Control and Status signals:

ALE (output) - Address Latch Enable.

It is an output signal used to give information of AD0-AD7 contents.

It is a positive going pulse generated when a new operation is started by uP.

When pulse goes high it indicates that AD0-AD7 are address.

When it is low it indicates that the contents are data.

RD (output 3-state, active low)

Read memory or IO device.

This indicates that the selected memory location or I/O device is to be read and that the data

bus is ready for accepting data from the memory or I/O device

WR (output 3-state, active low) Write memory or IO device.

This indicates that the data on the data bus is to be written into the selected memory location or I/O

device.

IO/M (output) - Select memory or an IO device.

This status signal indicates that the read / write operation relates to whether the memory or

I/O device.

It goes high to indicate an I/O operation.

It goes low for memory operations.

5. Status Signals:

S1: S2:

It is used to know the type of current operation of the microprocessor.

IO/M S1 S0 OPERATION

0 1 1 Opcode fetch

0 1 0 Memory read

0 0 1 Memory write

1 1 0 I/O read

1 0 1 I/O write

1 1 0 Interrupt acknowledge

Z 0 1 Halt

Z x x Hold

Z x x Reset

6. Interrupts and Externally initiated operations:

They are the signals initiated by an external device to request the microprocessor to do a particular

task or work.

There are five hardware interrupts called,TRAP

RST 7.5

RST 6.5

RST 5.5

INTA

On receipt of an interrupt, the microprocessor acknowledges the interrupt by the active low INTA

(Interrupt Acknowledge) signal.

Reset In (input, active low)

This signal is used to reset the microprocessor.

The program counter inside the microprocessor is set to zero.

The buses are tri-stated.Reset Out (Output)

It indicates CPU is being reset.

Used to reset all the connected devices when the microprocessor is reset.

7. Direct Memory Access (DMA): Tri state devices:

When 2 or more devices are connected to a common bus, to prevent the devices from interfering with

each other, the tristate gates are used to disconnect all devices except the one that is communicating at

a given instant.

The CPU controls the data transfer operation between memory and I/O device. Direct Memory Access

operation is used for large volume data transfer between memory and an I/O device directly.

The CPU is disabled by tri-stating its buses and the transfer is effected directly by external control

circuits.

HOLD signal is generated by the DMA controller circuit. On receipt of this signal, the microprocessor

acknowledges the request by sending out HLDA signal and leaves out the control of the buses. After the

HLDA signal the DMA controller starts the direct transfer of data. READY (input)

Memory and I/O devices will have slower response compared to microprocessors.

Before completing the present job such a slow peripheral may not be able to handle further data or

control signal from CPU.

The processor sets the READY signal after completing the present job to access the data.

The microprocessor enters into WAIT state while the READY pin is disabled.

8. Single Bit Serial I/O ports:

SID (input) Serial input data line

SOD (output) Serial output data line

These signals are used for serial communication.

Status Flags Sign Flag (S): It tells the sign of result stored in Accumulator after the operation is performed. If result is –ve, sign flag is set (1). If result is +ve, sign flag is reset (0).

After the execution of arithmetic or logical operations , if bit D7 of result is 1,the sign flag is

set . In a given byte if D7 is 1,the number will be viewed as negative number. If D7 is 0,the

number will be view as positive number.

In above example Data 1 is negative number because D7 is 1 and Data 2 are positive

because D7 is 0 as well as after performing addition operation D7 is 1 that represent that in

this case Sign flag is set and output will be negative number.

Zero Flag (Z): It tells whether the result stored in Accumulator is zero or not after the operation is performed. If result is zero, zero flag is set (1). If result is not zero, zero flag is reset (0). The zero flag sets if the result of operation in ALU is zero and flag resets if result is non

zero.The zero flag is also set if a certain register content becomes zero following an

increment or decrement operation of that register.

Suppose the Register B has content 1 after decrementing it will became zero in that case

also zero flag will be set.

In above example after performing addition of two data result is zero in that case Zero flag

will be set.

Auxiliary Carry Flag (AC): It is used in BCD operations. When there is carry in BCD addition, we add 0110 (6) to the result. If there is carry in BCD addition, auxiliary carry is set (1). If there is no carry, auxiliary carry is reset (0). The auxiliary carry flag is set when an auxiliary carry is generated in the process of

arithmetic operation in the accumulator. When a carry passes to D4 from bit D3 (from

lower nibble to higher nibble)in that case auxiliary carry flag will be set other wise reset.

This is also know as half carry.It may also occur in process of subtraction operation.This flag

is set if the subtraction operation results in borrow.This flag is used for BCD operations and

it is not available for programmer.

Parity Flag (P): It tells the parity of data stored in Accumulator. If parity is even, parity flag is set (1).

If parity is odd, parity flag is reset (0).

The parity flag is set if the content of the accumulator after an arithmetic operation has

even number of 1 .Otherwise parity flag will be reset.Parity defined by the number of 1 present in the accumulator

Carry (CS)

The carry status flag holds carry out of the most significant bit resulting from the execution of an arithmetic operation.

If there is a carry from addition or a borrow from subtraction or comparison, the carry flag CS is set to 1, otherwise 0.

The carry flag is set when a carry is generated in the process of an arithmetic operation in

the accumulator. When addition is carried out,it sometimes results in a ninth bit carried over

to next byte. The CY flag copies the value of the carry,which is an extra bit, from D7. It also

reflects the value of the borrow in subtraction.

In case of subtraction

Control Flag:- Out of nine active flags, six are conditional flags and the remaining three are

called as the control flag. The three control flags are:

1. The Trap flag(TF)

2. The interrupt flag(IF)

3. The direction flag(DF)

The Trap Flag: Setting TF puts the processor into single step mode for debugging, In single stepping

microprocessor executes a instruction and enters into single step ISR.

If TF=1, the CPU automatically generates an internal interrupt after each instruction,

allowing a program to be inspected as it executes instruction by instruction.

The Interrupt Flag:- If IF=1, the CPU will recognize external interrupt request (Interrupt Disabled). If IF=0, then

interrupt disabled.

Clearing IF disables these interrupts.

IF has no effect on either non-maskable external or internally generated interrupt.

The Direction Flag:- This bit is specially for string instructions.

If DF=1, the string instruction will automatically decrement the pointer. If DF=0,the string

instruction will automatically increment the pointer.

Draw the flag register format of 8085 microprocessor and explain all the flags. (Diagram–2Marks, Explanation–2Marks)

i) Carry flag (CY):

When µp performs addition/subtraction of 8 bit if the carry/borrow is generated from the MSB, then the carry flag is set (CY=1), otherwise it resets the carry flag (CY=0).

ii) Auxiliary carry flag (AC)/ Half carry/ Nibble carry:

When µp performs addition of 8 bit number and if the carry is generated from D3bit, then auxiliary carry flag is set, otherwise it is reset.

iii)Parity flag (P):

When µp performs addition or logical operations on 8 bit number and if number of

1„sbit in 8 bit result is even number, then it is called as Even parity and parity flag is

set (P=1) otherwise it is called as Odd parity and parity flag is reset (P=0).

iv)Zero Flag(Z):

When µp performs arithmetic and logical operation of two 8 bit numbers, if the result obtained is zero, then flag is set (Z=1),otherwise it is reset (Z=0).

v) Sign flag (S):

When µp performs arithmetic and logical operations on signed numbers and if the

MSB of the result is 1, then sign flag is set. i.e. for negative number sign flag is set

(S=1), otherwise it is reset (S=0).

Evolution of Microprocessor:

Microprocessor has turned into the brain of millions of gadgets, since year 1971 i.e.

devoid of microprocessors these wonderful innovations of millions of gadgets would

have not been possible. Now come have a look at the gadgets in which the

microprocessors are playing an imperative role from more than 40 long years.

Business Calculator: A business calculator was invented in the year 1971. The Unicom

141P business calculator was out of the foremost gadgets that feature a microprocessor.

Commodore PET: The PET was invented in the year 1971 and is broadly recognized as

the primary all-in-one home computer.

Washing Machine: The foremost microchip controlled washing machines were launched

in the year 1977 and gave a bang to the market, showcasing the varied usages of

innovative technology.

Arcade Mania in the year 1980: Namco pioneered Pac-Man in the walkways of the Unite

States and ignited a new trend.

Osborne 1 Laptop: With five screen and 10.7kgs of weight, Osborne 1 Laptop was

invented in the year 1981. It actually was the great grand-father of most modern laptops.

Nintendo NES: Consoles revitalized the gaming industry in the year 1986 such as

Nintendo Entertainment System.

Computing Democratized: Personal & business computing blasted with a broad variety

of laptops, desktops & even early tabs. These inventions came up in the year 1991.

MP3 Player: The modern way to enjoy to music forever altered in the last 1990s with the

foremost MP3 player, which was invented in the year 1997.

BlackBerry: The Smartphone insurgence boosted with the launch of RIM’s Blackberry

850. The 1st BB was accessible in the year 1999.

Apple iPod: Apple launched its 1st iPod in the year 2001; its release gave the future of

MP3 music format a new selection of set tunes.

Microsoft Windows Tablet: Approximately a decade prior to the shopper’s fascination

with tab, Microsoft Windows Tablet was launched in the year 2002, business were

employing these tabs for more useful jobs.

Netbook: Netbooks were launched in the year 2008, as small and light-weighted gadget

for carrying out uncomplicated jobs and enjoying media & internet content on the move.

Apple iPod: Tabs strike the customers main-stream with the release of iPod in the year

2010.

Digital Signage in the year 2011: Digital Signage was 1st of the vast new usages for the

microprocessor. Intellectual, internet allied gadgets are more and more found in the daily

life from business and retail to farming and automobiles.

Ultrabook in the year 2011: The advancement of the Personal Computer takes an

additional gigantic step as trendy Ultrabook gadgets push ahead high performance

computing experience.

Types and Specifications of Microprocessor:

Types of microprocessor:

There are basically 5 kinds of microprocessors namely:

Complex Instruction Set Microprocessors: They are also called as CISM in short and

they categorize a micro processor in which orders can be executed together along with

other low level activities. It mainly performs the task of uploading, downloading and

recalling data into and from the memory card. Apart from that it also does complex

mathematical calculations within a single command.

Reduced Instruction Set Microprocessor: This processor is also called as

RISC. These kinds of chips are made according to the function in which the

microprocessor can carry out small things within a particular command. In this way it

completes more commands at a faster rate.

Superscalar Processors: This is a processor that copies the hardware on the

microprocessor for performing numerous tasks at a time. They can be used for arithmetic

and as multipliers. They have several operational units and thus carry out more than a

one command by constantly transmitting various instructions to the superfluous

operational units inside the processor.

The Application Specific Integrated Circuit: This processor is also known as ASIC.

They are used for specific purposes that comprises of automotive emissions control or

personal digital assistants computer. This kind of processor is made with proper

specification but apart from that it can also be made using the off the shelf gears.

Digital Signal Multiprocessors: Also called as DSP’s, these are used for encoding and

decoding videos or to convert the digital and video to analog and analog to digital. They

need a microprocessor that is excellent in mathematical calculations. The chips of this

processor are employed in SONAR, RADAR, home theaters audio gears, Mobile phones

and TV set top boxes.

Microprocessor Specifications:

External and Internal Data Bus: The most initial microprocessors could handle

information only in 8 bits. As the width of the data bus increases it determines the amount

of information that can be moved in and out in a single operation. Apart from that it also

states the amount of instructions and numbers that can be used. Also the width of the

internal bus and storage area differs from the external bus. Thus it differs from company

to company. However the Pentium processors have an external 64 bit data bus.

Cache Memory: When the speed of the processor increases the RAM finds it difficult to

withstand it. Thus to minimize the size and the cost, RAM uses dynamic RAM which is

faster in one hand while on the other very expensive. Thus it is used less for temporary

storage of files on the microprocessor this is called as cache memory. It is also called as

high speed memory and is operated by a cache controller that identifies which data and

instruction would be required for the next and accordingly loads it into the cache.

Speed of Clock: The oscillator that is fixed above the motherboard generates a number

of electronic pulses that is used by the computer to synchronize operations. The change

in the signal from positive to negative and vice versa is a cycle and thus the amount of

cycle per second is calculated in hertz. The processor’s speed is generally the multiple of

the external bus.

MIPS: A microprocessor generally requires 10 clocks cycle to complete a single

instruction. Also the speed of the clock does not relate directly to the speed at which the

CPU processes the instructions. To measure more than one instruction at a time modern

processors have multiple pipelines, however apart from this a more accurate way to

measure the speed of the processor is with the help of MIPS (Millions of instructions per

second).

Power Consumption: Power consumption is also a way of measuring the performance

of the microprocessor. The formula for this is volts X Amps = watts. If the power

consume id much then it is give as heat and if there is low consumption it helps in

increasing the batter life of notebook computers.

8085 Microprocessor:

This was introduced by the Intel Company in the year 1977 to 1990. It was compatible

with Intel 8080 but needed less support of the hardware. The 5 in the model was added

as it requires plus 5 voltages. Minus 5 voltage and plus 12 voltage. It is an 8 bit general

purpose microprocessor that can easily store 64k bite of memory. These were used in

computers that used the CP or M operating system.

Microprocessor and Interfacing:

A microprocessor to become a more useful device needs to be connected to other

electronic device. In order to design a computer the microprocessor needs to be

interfaced to the main memory, keyboard, USB ports, disk memory etc. now in this

process of interfacing we come across two types namely Memory Interfacing and I/O

Interfacing.

Memory interfacing: The microprocessor needs to access memory for the purpose of

reading instructions and codes stored in the memory the memory requires a set of signals

to read from and write to the registers. The same way the microprocessor too transmits

signals for the purpose of data reading and writing. The process of interfacing here

requires the match the requirement of the memory with the signals of the microprocessor.

Thus, it should be designed in such a way that both of these match thus the primary

purpose of the memory interfacing is to to help the microprocessor in reading and writing

data at the given register of the chip.

I/O Interfacing: The keyboard and the displays need to be interfaced with the

microprocessor as it is used as a channel of communication. This is called as I/O

interfacing. Latches and buffers are used in this type for interfacing keyboards and

displays with the microprocessor. However one drawback in this method is that it can just

perform a single function. It performs as an input device when connected to the buffer and

as an output device when connected to the latch. Thus this interfacing has a limited

capability.

Advantages and Disadvantages of Microprocessors

The advantages of microprocessors are

o The processing speed is high

o Intelligence has been brought to systems

o Flexible.

o Compact size.

o Easy maintenance

o Complex mathematics

Some of the disadvantages of microprocessor are it might get overheated and the limitation of the

microprocessor imposes on size of data.

The applications of the microprocessors mainly involve in controllers in home appliances, wireless

communication equipment’s, office publication and automation, consumer electronic goods,

calculators, accounting system, video games, industrial controllers and data acquisition systems.

Disadvantages

Some of the disadvantages with the Microprocessor are that it might get over-heated, and the

limitation it imposes on the size of data.

Applications of Microprocessors

Microprocessors are a mass storage device. They are the advanced form of computers. They arealso

called as microcomputers. The impact of microprocessor in different lures of fields is significant. The

availability of low cost, low power and small weight, computing capability makes it useful in different

applications. Now a days, a microprocessor based systems are used in instructions, automatic testing

product, speed control of motors, traffic light control , light control of furnaces etc. Some of the

important areas are mentioned below:

Instrumentation:

it is very useful in the field of instrumentation. Frequency counters, function generators, frequency

synthesizers, spectrum analyses and many other instruments are available, when microprocessors are

used as controller. It is also used in medical instrumentation.

Control:

Microprocessor based controllers are available in home appliances, such as microwave oven, washing

machine etc., microprocessors are being used in controlling various parameters like speed, pressure,

temperature etc. These are used with the help of suitable transduction.

Communication:

Microprocessors are being used in a wide range of communication equipments. In telephone

industry, these are used in digital telephone sets. Telephone exchanges and modem etc. The use of

microprocessor in television, satellite communication have made teleconferencing possible. Railway

reservation and air reservation system also uses this technology. LAN and WAN for communication

of vertical information through computer network.

Office Automation and Publication:

Microprocessor based micro computer with software packages has changed the office environment.

Microprocessors based systems are being used for word processing, spread sheet operations,

storage etc. The microprocessor has revolutionize the publication technology.

Consumer:

The use of microprocessor in toys, entertainment equipment and home applications is making them

more entertaining and full of features. The use of microprocessors is more widespread and popular.

Now the Microprocessors are used in :

1. Calculators

2. Accounting system

3. Games machine

4. Complex Industrial Controllers

5. Traffic light Control

6. Data acquisition systems

7. Multi user, multi-function environments

8. Military applications

9. Communication systems

Features of 8085

It is an 8 bit microprocessor (each character is represented by 8 bits or a byte).

It is manufactured with N-MOS (n-type Metal Oxide Semiconductor) technology implemented with

6200 transistors.

It has 16-bit address lines - A0-A15 (to point the memory locations) and hence can point up to 2^16 =

65535 bytes (64KB) memory locations.

The first 8 lines of address bus and 8 lines of data bus are multiplexed AD0-AD7. Data bus is a group of

8 lines D0-D7.

It provides 5 level interrupts and supports external interrupt request.

A 16 bit program counters (PC).

A 16 bit stack pointer (SP).

It provides 1 accumulator, 2 flag register, six 8-bit general purpose register arranged in pairs: BC, DE,

HL and 2special purpose registers.

It consists of 74 instruction sets.

It performs arithmetic and logical operations.

It provides status for advanced control signals, On chip clock generator.

It requires a signal +5V power supply and operates at 3.2 MHZ single phase clock with maximum clock

frequency 6 MHz and minimum clock frequency 500 kHz.

Serial input/output port.

1.3 micro sec instruction cycles.

It is enclosed with 40 pins DIP (Dual in line package).

It can be used to implement (interface) 3 chip micro-computers (8085, 8155, 8255 and 8355:

Peripheral IC's).