Machine Code and Assembly Language.pptx

7/29/2019 Machine Code and Assembly Language.pptx

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01110111011010001000

MOV A

JMP B


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What is a programming language?

A programming language is a notational system for

describing computation in a machine-readable andhuman-readableform.

To build programs, people use languages that are similar

to human language. The results are translated intomachine code, which computers understand.


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Classification of the languages

Programming languages fall into three broad categories:

Machine languages

Assembly languages

Higher-level languages

In the formal classification the above 3 categories are

divided into as 5 Generations of languages.


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Generations of Programming

Languages1stGL: machine codes

2ndGL: symbolic assemblers

3rd

GL: (machine-independent) imperative languages(FORTRAN, Pascal, C ...)

4th GL: domain specific application generators

5th GL: AI languages

Each generation is at a higher level of abstraction

i.e.: The higher the generation, the lesser the programmer willbe aware of the internal workings of the program in thehardware level.


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A Brief ChronologyEarly 1950s order codes (primitive assemblers)

1957 FORTRAN the first high-level programming language

1958 ALGOL the first modern, imperative language

1960 LISP, COBOL Interactive programming; business programming

1962 APL, SIMULA the birth of OOP (SIMULA)

1964 BASIC, PL/I

1966 ISWIM first modern functional language (a proposal)1970 Prolog logic programming is born

1972 C the systems programming language

1975 Pascal, Scheme two teaching languages

1978 CSP Concurrency matures

1978 FP Backus proposal

1983 Smalltalk-80, Ada OOP is reinvented

1984 Standard ML FP becomes mainstream (?)1986 C++, Eiffel OOP is reinvented (again)

1988 CLOS, Oberon, Mathematica

1990 Haskell FP is reinvented

1990s Perl, Python, Ruby, JavaScript Scripting languages become mainstream

1995 Java OOP is reinvented for the internet

2000 C#


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What is Machine Code ?

Machine code is the only form of program instructions that

the computer hardware can understand and execute directly.

All other forms of computer language must be translated into

machine code in order to be executed by the hardware.

Machine code consists of many strings ofbinary digits that are

easy for the computer to interpret, but tedious for human

beings to interpret.

Machine code is different for each type of computer.

A program in machine code for an Intel x86-based PC will not run

on an IBM mainframe computer, and vice versa.


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Assembly Language Assembly language is a symbolic representation of machine

code, which allows programmers to write programs inmachine code without having to deal with the long binarystrings.

For example, the machine code for an instruction that addstwo numbers might be 01101110, but in assembly language,this can be represented by the symbol ADD.

A simple assembler program translates this symbolic languagedirectly into machine code.

Because machine code is specific to each type of computerhardware, assembly languages are also specific to each type ofcomputer.

However, all machine languages and assembly languages lookvery similar, even though they are not interchangeable.


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Assembler

Assembly

code

Object code


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High Level Languages High-level language is a language that is convenient for human

beings to understand.

High-level programming languages must be translated into machinecode for execution, and this process is called compilation.

A program that carries out this translation is a compiler. High-level language may bear no resemblance at all to machine

code.

The compiler figures out how to generate machine language thatdoes exactly what the high-level-language source program specifies.

Languages like C++, Algol, COBOL, etc., are all compiled high-levellanguages.

They usually work more or less the same across all computer types,which makes them much more portable than assembly language.


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Higher-Level Languages -

Third-Generation Languages Third-generation languages (3GLs) are the first to use true English-

like phrasing, making them easier to use than previous languages.

3GLs are portable, meaning the object code created for one type ofsystem can be translated for use on a different type of system.

The following languages are 3GLs:

FORTAN C

COBOL C++

BASIC Java

Pascal ActiveX


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Example :


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Higher-Level Languages -

Fourth-Generation Languages Fourth-generation languages (4GLs) are even easier to use

than 3GLs.

4GLs may use a text-based environment (like a 3GL) or mayallow the programmer to work in a visual environment, usinggraphical tools.

The following languages are 4GLs: Visual Basic (VB)

VisualAge

Authoring environments


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Why we need assembly langauge?

Early computer systems were literally programmed by hand.

Front panel switches were used to enter instructions and data.

These switches represented the address, data and control lines

of the computer system. To enter data into memory, the address switches were toggled

to the correct address, the data switches were toggled next,and finally the WRite switch was toggled.

This wrote the binary value on the front panel data switches tothe address specified.

Once all the data and instruction were entered, the run switchwas toggled to run the program.


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With the advent of better hardware which could address

larger memory, and the increase in memory size (due tobetter production techniques and lower cost), programs

were written to perform some of this manual entry.

Small monitor programs became popular, which allowedentry of instructions and data via hex keypads or

terminals.

Additional devices such as paper tape and punched cards

became popular as storage methods for programs.


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Programs were still hand-coded, in that the conversion

from mnemonics to instructions was still performedmanually.

To increase programmer productivity, the idea of writing

a program to interpret another was a major

breakthrough.

This would be run by the computer, and translate the

actual mnemonics into instructions.

The benefits of such a program would be reduced errors

faster translation times

changes could be made easier and faster


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Mnemonics AssemblerMachine

Code

Assembly language programming is writing machine

instructions in mnemonic form, using an assembler to

convert these mnemonics into actual processor

instructions and associated data.

So basically assembly language is a translator from

human world to the machine world.


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Disadvantages of assembly

language programming

the programmer requires knowledge of the processor

architecture and instruction set

many instructions are required to achieve small tasks.

source programs tend to be large and difficult to follow

programs are machine dependent, requiring complete

rewrites if the hardware is changed


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Software development process

The Real WorldProblem

Logical Solution(On paper)

Selecting tools

(programminglanguage/method)

Coding

Testing/Debugging

Release as finalsolution


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The program translation sequence

Developing a software program to accomplish a particular

task : -

the implementer chooses an appropriate language,

develops the algorithm (a sequence of steps, which when

carried out in the order prescribed, achieve the desired

result),

implements this algorithm in the chosen language (coding),

then tests and debugs the final result.


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Software execution process

Machine code or the executable codewhich the machine understands


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Assembly language programming Features provided by an assembler are,

allows the programmer to use mnemonics when writing source codeprograms.

variables are represented by symbolic names, not as memory locations

symbolic code is easier to read and follow

error checking is provided

changes can be quickly and easily incorporated with a re-assembly

programming aids are included for relocation and expression evaluation

In writing assembly language programs for micro-computers, it isessential that a standardized format be followed. Mostmanufacturers provide assemblers, which are programs used togenerate machine code instructions for the actual processor toexecute.


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The assembler converts the written assembly

language source program into a format which run on theprocessor.

Each machine code instruction (the binary or hex value) is

replaced by a mnemonic.

A mnemonic is an abbreviation which represents theactual instruction.

Binary Hex Mnemonic

01001111 4F CLRA Clears the A accumulator00110110 36 PSHA Saves A acc on stack

01001101 4D TSTA Tests A acc for 0


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Assembly language statements are written one per line.

A machine code program thus consists of a sequence of

assembly language statements, where each statement

contains a mnemonic.

Each line of an assembly language program is split intofour fields, as shown below

LABEL OPCODE OPERAND COMMENTS


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Label The label field is optional.

A label is an identifier (or text string symbol).

Labels are used extensively in programs to reduce reliance upon

programmers remembering where data or code is located. A label can be used to refer to a memory location the value of a

piece of data the address of a program, sub-routine, code portionetc.

The maximum length of a label differs between assemblers. Some

accept up to 32 characters long, others only four characters.

A label, when declared, is suffixed by a colon, and begins with a validcharacter (A..Z).


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Example

START: LDAA #24H

Here, the label START is equal to the address of the instruction LDAA#24H.

The label is used in the program as a reference,eg,

JMP START

This would result in the processor jumping to the location (address)associated with the label START, thus executing the instruction LDAA#24H immediately after the JMP instruction. When a label isreferenced later on in the program, it is done so without the colonsuffix.


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Machine Code and Assembly Language.pptx

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