Detailed Contents :-1.Evolution of Microprocessor

Typical organization of a microcomputer system and functions of its various blocks.

Microprocessor, its evolution, function and impact on modern society.

2.Architecture of a Microprocessor (With reference to 8085 microprocessor) Concept of Bus, bus organization of 8085, Functional block diagram of 8085 and

function of each block, Pin details of 8085 and related signals, Demultiplexing of

address/data bus generation of read/write control signals, Steps to execute a stored

programme.

3.Instruction Timing and Cycles Instruction cycle, machine cycle and T-states, Fetch and execute cycle.

4.Programming (with respect to 8085 microprocessor)Brief idea of machine and assembly languages, Machines and Mnemonic codes.

Instruction format and Addressing mode.

Identification of instructions as to which addressing mode they belong. Concept of

Instruction set. Explanation of the instructions of the following groups of instruction set.

Data transfer group, Arithmetic Group, Logic Group, Stack, I/O and Machine Control

Group. Programming exercises in assembly language. (Examples can be taken from the

list of experiments).

5.Memories and I/O interfacing

Concept of memory mapping, partitioning of total memory space. Address decoding,

concept of peripheral mapped I/O and memory mapped I/O. Interfacing of memory

mapped I/O devices.

6.Interrupts

Concept of interrupt, Maskable and non-maskable, Edge triggered and level triggered

interrupts, Software interrupt, Restart interrupts and its use, Various hardware interrupts

of 8085, Servicing interrupts, extending interrupt system.

7.Data Transfer Techniques

Concept of programmed I/O operations, sync data transfer, async data transfer (hand

shaking), Interrupt driven data transfer, DMA, Serial output data, Serial input data.

8.Peripheral devices

8255 PPI, 8253 PIT,8279 and 8257 DMA controller.

Microprocessor 8085 :- 1st Generation: This was the period during 1971 to 1973 of microprocessor’s

history. In 1971, INTEL created the first microprocessor 4004 that would run at a

clock speed of 108 KHz. During this period, the other microprocessors in the

market including Rockwell international PPS-4, INTEL-8008 and National

semiconductors IMP-16 were in use. But, all these were not TTL compatible

processors.

2nd Generation: This was the period during 1973 to 1978 in which very efficient

8-bit microprocessors were implemented like Motorola 6800 and 6801, INTEL-

8085 and Zilogs-Z80, which were among the most popular ones. Owing to their

superfast speed, they were costly as they were based on NMOS fabrication

technology.

3rd Generation: During this period 16 bit processors were created and designed

using HMOS technology. From 1979 to 1980, INTEL 8086/80186/80286 and Motorola

68000 and 68010 were developed. Speeds of those processors were four times better

than the 2nd generation processors.

4th Generation: From 1981 to 1995 this generation developed 32 bit

microprocessors by using HCMOS fabrication. INTEL-80386 and Motorola’s

68020/68030 were the popular processors.

5th Generation: From 1995 to until now this generation has been bringing out high-

performance and high-speed processors that make use of 64-bit processors. Such

processors include Pentium, Celeron, Dual and Quad core processors.

Bus Organisation of 8085 :-There are three buses in Microprocessor :-

1.Address Bus

2.Data Bus

3.Control Bus

1. Address Bus:- Microprocessor has 16 bit address bus. The bus over which the

CPU sends out the address of the memory location is known as Address bus. The

address bus carries the address of memory location to be written or to be read from.

The address bus is unidirectional. It means bits flowing occurs only in one direction,

only from microprocessor to peripheral devices.

We can find that how much memory location it can using the formula 2^N. where N

is the number of bits used for address lines.

here, 2^16 = 65536bytes or 64Kb

So we can say that it can access upto 64 kb memory location.

2. Data Bus:-8085 Microprocessor has 8 bit data bus. So it can be used to carry the 8

bit data starting from 00000000H(00H) to 11111111H(FFH). Here 'H' tells the

Hexadecimal Number. It is bidirectional. These lines are used for data flowing in both

direction means data can be transferred or can be received through these lines. The

data bus also connects the I/O ports and CPU. The largest number that can appear

on the data bus is 11111111.

It has 8 parallel lines of data bus. So it can access upto 2^8 = 256 data bus lines.

3. Control Bus:-The control bus is used for sending control signals to the

memory and I/O devices. The CPU sends control signal on the control bus to

enable the outputs of addressed memory devices or I/O port devices.

Some of the control bus signals are as follows:

1. Memory read

2. Memory write

3. I/O read

4. I/O write.

Microprocessor 8085 :- 8085 is pronounced as "eighty-eighty-five" microprocessor. It is an 8-bit

microprocessor designed by Intel in 1977 using NMOS technology.

It has the following configuration −

8-bit data bus

16-bit address bus, which can address upto 64KB

A 16-bit program counter

A 16-bit stack pointer

Six 8-bit registers arranged in pairs: BC, DE, HL

Requires +5V supply to operate at 3.2 MHZ single phase clock

It is used in washing machines, microwave ovens, mobile phones, etc.

8085 Architecture:-

8085 Microprocessor – Functional Units :-8085 consists of the following functional units −

▪AccumulatorIt is an 8-bit register used to perform arithmetic, logical, I/O & LOAD/STORE

operations. It is connected to internal data bus & ALU.

▪Arithmetic and logic unitAs the name suggests, it performs arithmetic and logical operations like Addition,

Subtraction, AND, OR, etc. on 8-bit data.

▪General purpose registerThere are 6 general purpose registers in 8085 processor, i.e. B, C, D, E, H & L. Each

register can hold 8-bit data.

These registers can work in pair to hold 16-bit data and their pairing combination is

like B-C, D-E & H-L.

▪Program counterIt is a 16-bit register used to store the memory address location of the next instruction

to be executed. Microprocessor increments the program whenever an instruction is

being executed, so that the program counter points to the memory address of the next

instruction that is going to be executed.

▪Stack pointerIt is also a 16-bit register works like stack, which is always incremented/decremented

by 2 during push & pop operations.

▪Temporary registerIt is an 8-bit register, which holds the temporary data of arithmetic and logical

operations.

▪Flag registerIt is an 8-bit register having five 1-bit flip-flops, which holds either 0 or 1 depending

upon the result stored in the accumulator.

These are the set of 5 flip-flops −

Sign (S)

Zero (Z)

Auxiliary Carry (AC)

Parity (P)

Carry (C)

Its bit position is shown in the following table −

D7 D6 D5 D4 D3 D2 D1 D0

S Z AC P CY

▪Instruction register and decoderIt is an 8-bit register. When an instruction is fetched from memory then it is stored in

the Instruction register. Instruction decoder decodes the information present in the

Instruction register.

▪Timing and control unitIt provides timing and control signal to the microprocessor to perform operations.

Following are the timing and control signals, which control external and internal

circuits −

Control Signals: READY, RD’, WR’, ALE

Status Signals: S0, S1, IO/M’

DMA Signals: HOLD, HLDA

RESET Signals: RESET IN, RESET OUT

▪Interrupt controlAs the name suggests it controls the interrupts during a process. When a

microprocessor is executing a main program and whenever an interrupt occurs, the

microprocessor shifts the control from the main program to process the incoming

request. After the request is completed, the control goes back to the main program.

There are 5 interrupt signals in 8085 microprocessor: INTR, RST 7.5, RST 6.5,

RST 5.5, TRAP.

▪Serial Input/output controlIt controls the serial data communication by using these two instructions: SID

(Serial input data) and SOD (Serial output data).

▪Address buffer and address-data bufferThe content stored in the stack pointer and program counter is loaded into the

address buffer and address-data buffer to communicate with the CPU. The

memory and I/O chips are connected to these buses; the CPU can exchange the

desired data with the memory and I/O chips.

Address bus and data bus

Data bus carries the data to be stored. It is bidirectional, whereas address bus

carries the location to where it should be stored and it is unidirectional. It is used

to transfer the data & Address I/O devices.

8085 Pin Configuration:-

Different Cycles of 8085 :-Instruction Cycle :- The Steps required by CPU to fetch and execute an Instruction is called a Instruction Cycle. It consist of fetch and Execute Cycle.

Instruction Cycle=Fetch Cycle + Execute CycleMachine Cycle :- It is a time Required by microprocessor to complete the operation of accessing memory or I/O devices is called machine cycle. It perform specific operation like opcode fetch, memory read, write, I/O read/write are performed in machine cycle.The machine cycle is a 4 process cycle that includes reading and interpreting the machine language, executing the code and then storing that code.

Four steps of Machine cycle

Fetch - Retrieve an instruction from the memory.

Decode - Translate the retrieved instruction into a series of computer commands.

Execute - Execute the computer commands.

Store - Send and write the results back in memory.

Clock cycle :- The speed of a computer processor, or CPU, is determined by

the clock cycle, which is the amount of time between two pulses of an oscillator.

Generally speaking, the higher number of pulses per second, the faster the

computer processor will be able to process information. The clock speed is

measured in Hz, typically either megahertz (MHz) or gigahertz (GHz). For

example, a 4GHz processor performs 4,000,000,000 clock cycles per second.

Computer processors can execute one or more instructions per clock cycle,

depending on the type of processor. Early computer processors and slower

processors can only execute one instruction per clock cycle, but faster, more

advanced processors can execute multiple instructions per clock cycle,

processing data more efficiently.

T state :- It is defined as the one subdivision of operation performed in one

clock period. One complete cycle of clock is called as T-state as shown in the

below figure. The time intervals T1T1 orT2T2 are the examples of T-state. A T-

state is measured from the falling edge of one clock pulse to the falling edge of

the next clock pulse. Various versions of 8086 have maximum clock frequency

from 5MHz to 10MHz. Hence the minimum time for one T-state is between 100

to 200 n sec.

Brief Idea of Languages :-Machine Language:- The machine language is the internal language of the

computer system. It is a difficult programming language to handle by any humans.

It is usually made up of a binary string of 0s and 1s that is understood by the

machine to follow any instructions. Infact, we can say that the machine can only

recognize these 0s and 1s and nothing else. So, it is a language of the lowest degree

made for machines only. Programmes therefore prefers to use either a high-level

programming language or an assembly language to deliver various instructions by

translating it to machine understandable codes known as machine codes.

Assembly Language:- Assembly language is a second generation programming

language used in the computer systems. In assembly language, a programmer uses

symbolic instructions instead of machine language instructions and descriptive

names for data items and memory location.

An assembly language program is written according to strict rules and then

translated by an assembler into machine code. It is machine dependant language

hence it is not portable. It has very less restrictions and also features high

interaction between the operating system and the hardware thus enabling to write

easy hardware dependant programs. The various symbolic notations used in the

assembly language is called mnemonics.

High Level Language :- Sometimes abbreviated as HLL, a high-level language is

a computer programming language that isn't limited by the computer, designed

for a specific job, and is easier to understand. It is more like human language and

less like machine language. However, for a computer to understand and run a

program created with a high-level language, it must be compiled into machine

language.

The first high-level languages were introduced in the 1950's. Today, high-level

languages are in widespread use. These

include BASIC, C, C++, Cobol, FORTRAN, Java, Pascal, Perl, PHP and Visual

Basic.

Addressing Modes of 8085:-(i)Immediate Addressing mode :- In this mode operand is a part of the

instruction itself is known as Immediate Addressing mode. If the immediate

data is 8-bit, the instruction will be of two bytes. If the immediate data is 16 bit,

the instruction is of 3 bytes.

Ex: (1). ADI DATA ; Add immediate the data to the contents of the

accumulator.

(2).LXIH 8500H : Load immediate the H-L pair with the operand 8500H

(3). MVI 08H ; Move the data 08 H immediately to the accumulator

(4). SUI 05H ; Subtract immediately the data 05H from the accumulator

(ii) Direct Addressing mode:- The mode of addressing in which the 16-bit

address of the operand is directly available in the instruction itself is called

Direct Addressing mode. i.e., the address of the operand is available in the

instruction itself. This is a 3-byte instruction.

Ex: (1). LDA 9525H; Load the contents of memory location into Accumulator.

(2). STA 8000H; Store the contents of the Accumulator in the location 8000H

(3). IN 01H; Read the data from port whose address is 01H.

(iii). Register addressing modes:- In this mode the operands are

microprocessor registers only. i.e. the operation is performed within various

registers of the microprocessor.

Ex: (1). MOV A, B; Move the contents of B register to A register.

(2). SUB D; Subtract the contents of D register from Accumulator.

(3). ADD B, C; Add the contents of C register to the contents of B register.

(iv). Register indirect addressing modes:- The 16-bit address location of the

operand stored in a register pair (H-L) is given in the instruction. The address

of the operand is given in an indirect way with the help of a register pair. So it is

called Register indirect addressing mode.

Ex: (1). LXIH 9570H : Load immediate the H-L pair with the address of the

location 9570H.

MOV A, M : Move the contents of the memory location pointed by the H-L

pair to accumulator.

(v). Implicit Addressing mode:- The mode of instruction which do not specify the

operand in the instruction but it is implicated, is known as implicit addressing mode.

i.e., the operand is supposed to be present generally in accumulator.

Ex: (1).CMA; complement the contents of Accumulator

(2).CMC; Complement carry

(3). RLC; Rotate Accumulator left by one bit

(4). RRC; Rotate Accumulator right by one bit

(5). STC; Set carry.

Instruction Set of 8085 :-An instruction is a binary pattern designed inside a microprocessor to perform a

specific function. The entire group of instructions, called the instruction set, determines

what functions the microprocessor can perform. These instructions can be classified into

the following five functional categories: data transfer (copy) operations, arithmetic

operations, logical operations, branching operations, and machine-control operations.

1. Data Transfer Group :- The data transfer instructions move data between

registers or between memory and registers.

MOV Move

MVI Move Immediate

LDA Load Accumulator Directly from Memory

STA Store Accumulator Directly in Memory

LHLD Load H & L Registers Directly from Memory

SHLD Store H & L Registers Directly in Memory

An 'X' in the name of a data transfer instruction implies that it deals with a

register pair (16-bits);

LXI Load Register Pair with Immediate data

LDAX Load Accumulator from Address in Register Pair

STAX Store Accumulator in Address in Register Pair

XCHG Exchange H & L with D & E

XTHL Exchange Top of Stack with H & L

2. Arithmetic Group :- The arithmetic instructions add, subtract, increment, or

decrement data in registers or memory.

ADD Add to Accumulator

ADI Add Immediate Data to Accumulator

ADC Add to Accumulator Using Carry Flag

ACI Add immediate data to Accumulator Using Carry

SUB Subtract from Accumulator

SUI Subtract Immediate Data from Accumulator

SBB Subtract from Accumulator Using Borrow (Carry) Flag

SBI Subtract Immediate from Accumulator Using Borrow (Carry)

Flag

INR Increment Specified Byte by One

DCR Decrement Specified Byte by One

INX Increment Register Pair by One

DCX Decrement Register Pair by One

DAD Double Register Add; Add Content of Register

Pair to H & L Register Pair

3. Logical Group :- This group performs logical (Boolean) operations on data in

registers and memory and on condition flags. The logical AND, OR, and Exclusive OR

instructions enable you to set specific bits in

the accumulator ON or OFF.

ANA Logical AND with Accumulator

ANI Logical AND with Accumulator Using Immediate Data

ORA Logical OR with Accumulator

OR Logical OR with Accumulator Using Immediate Data

XRA Exclusive Logical OR with Accumulator

XRI Exclusive OR Using Immediate Data

The Compare instructions compare the content of an 8-bit value with the contents of the

accumulator;

CMP Compare

CPI Compare Using Immediate Data

The rotate instructions shift the contents of the accumulator one bit position to the left

or right:

RLC Rotate Accumulator Left

RRC Rotate Accumulator Right

RAL Rotate Left Through Carry

RAR Rotate Right Through Carry

Complement and carry flag instructions:

CMA Complement Accumulator

CMC Complement Carry Flag

STC Set Carry Flag

4. Branch Group :- The branching instructions alter normal sequential program flow,

either unconditionally or

conditionally. The unconditional branching instructions are as follows:

JMP Jump

CALL Call

RET Return

Conditional branching instructions examine the status of one of four condition flags to

determine

whether the specified branch is to be executed. The conditions that may be specified are

as follows:

NZ Not Zero (Z = 0)

Z Zero (Z = 1)

NC No Carry (C = 0)

C Carry (C = 1)

PO Parity Odd (P = 0)

PE Parity Even (P = 1)

P Plus (S = 0)

M Minus (S = 1)

Thus, the conditional branching instructions are specified as follows:

Jumps Calls Returns Condition

INC CNC RNC (No Carry)

JNZ CNZ RNZ (Not Zero)

JM CM RM (Minus)

JP0 CPO RPO (Parity Odd)

JM CM RM (Minus)

JPE CPE RPE (Parity Even)

JP0 CPO RPO (Parity Odd)

Two other instructions can affect a branch by replacing the contents or the program

counter:

PCHL Move H & L to Program Counter

RST Special Restart Instruction Used with Interrupts

5. Stack Instructions :- The following instructions affect the Stack and/or Stack

Pointer

PUSH Push Two bytes of Data onto the Stack

POP Pop Two Bytes of Data off the Stack

XTHL Exchange Top of Stack with H & L

SPHL Move content of H & L to Stack Pointer

6. I/O instructions :-

IN Initiate Input Operation

OUT Initiate Output Operation

7. Machine Control instructions :-

EI Enable Interrupt System

DI Disable Interrupt System

HLT Halt

NOP No Operation

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