3 - assemby language programming for microprocessor

8/9/2019 3 - Assemby Language Programming for Microprocessor

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Fundamental of Assembly LanguageProgramming (for Microprocessor)

Prima Dewi PurnamasariMicroprocessor

Electrical Engineering Department

Universitas Indonesia


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Computer Language

High Level language Pascal, C, C++, Java, etc

Low Level Language

Assembly

Machine Codes 010010001010100101010 in binary

1234 FFAB 1234 H in hexadecimal

2 Microprocessor (c) Prima Dewi Purnamasari 2011


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Why Assembly?

Assembly has several features that make it a good choice manysome situations.

1. It's fast – Assembly programs are generally faster than

programs created in higher level languages. Often,programmers write speed-essential functions in assembly.

2. It's powerful – You are given unlimited power over your

assembly programs. Sometimes, higher level languages haverestrictions that make implementing certain things difficult.

3. It's small – Assembly programs are often much smaller

than programs written in other languages. This can be veryuseful if space is an issue.



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Preparation for Assembly Programming

Basically you will need: Program editor as simple as Notepad

Assembler

1. MASM http://www.masm32.com/.

2.

TASM

Made by Borland, a commercial product3. NASM http://sourceforge.net/projects/nasm/

Be careful in writing your programs, because it runs directlyon your microprocessor!


http://www.masm32.com/http://sourceforge.net/projects/nasm/http://sourceforge.net/projects/nasm/http://www.masm32.com/


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Steps to Create a

Program



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Creating an Assembly Language Program

An assembly language program should be written with anytext editor and have the extension filename.asm.

The assembler and Linker

The assembler program converts a symbolic source module

(file) into a hexadecimal object file The linker program executes as the second part of ML, reads the

object files, created by the assembler program, and links them intoa single execution file (.EXE)



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MASM32



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TASM



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Emulator

anemulator

is hardware and/or software that duplicates (oremulates) the functions of a first computer system in a different

second computer system, so that the behavior of the second

system closely resembles the behavior of the first system.



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Emu8086



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Individual Assignment

Download and install emu8086 (trial)

http://www.emu8086.com/

Find corresponding tutorial on how to use it (available on the

Internet!), self study!


http://www.emu8086.com/http://www.emu8086.com/


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Group assignment

Each group is responsible to bring at minimum 1 laptop(with emu8086 installed) to class every session



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Assembly Program Structure



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LIST File, generated

automatically after

program successfullyassembled

MachinecodesMemoryAddress



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Writing Structure

NEXT: MOV AX, [BX] ; comment

1= label, followed by “:”

2= opcode 3= operand

4= comment, preceded with”;”

1 432



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Writing Structure

Each statement in an assembly language program consistsof four parts or fields.

The leftmost field is called the label.

used to store a symbolic name for the memory location it

represents

All labels must begin with a letter or one of the following

special characters: @, $, -, or ?.

a label may have any length from 1 to 35 characters

The label appears in a program to identify the name of a

memory location for storing data and for other

purposes.



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The next field to the right is the opcode field. designed to hold the instruction, or opcode

the MOV part of the move data instruction is an exampleof an opcode

Right of the opcode field is the operand field. contains information used by the opcode

the MOV AL,BL instruction has the opcode MOV andoperands AL and BL

The comment field, the final field, contains a comment aboutthe instruction(s).

comments always begin with a semicolon (;)



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Try it in emulator! Click “View” and look the changes in every menu list:

registers

Data

Screen Flags

etc



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Computer Data Formats

Microprocessor (c) Prima Dewi Purnamasari 201121


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Computer Data Formats

ASCII and Unicode Data Binary Coded Decimal (BCD)

Byte-Sized Data

Word-Sized Data

Doubleword-Sized Data

Real Numbers



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ASCII Data

American Standard Code for Information Interchange(ASCII) data represent alphanumeric characters in thememory of a computer system (Table 1.7)

The standard ASCII code is a 7-bit code with the eighth and

MSB used to hold parity in some systems ASCII are most often stored in memory using a special

directive to the assembler program called define byte(s) or DB



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BCD Data

Binary-Coded Decimal (BCD) information is stored ineither packed or unpacked forms

Packed BCD data are stored as two digits per byte

Unpacked BCD data are stored as one digit per byte

The range of a BCD digit extends from 00002 to 10012 or0-9 decimal

Table 1.9 shows some decimal numbers converted to bothpacked ad unpacked BCD



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Byte-Sized Data

Byte-size data are stored as unsigned and signed integers Negative signed numbers are stored in the 2’s complement

form

Whenever a number is 2’s complement, its sign changes from

negative to positive or positive to negative See example 1-22, 1-23



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Define byte (DB) directive is used to store 8-bit data

in memory

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Word-sized Data

A word (16-bits) is formed with two bytes of data

The LSB is always stored in the lowest-numbered memorylocation, the MSB in the highest (i.e., little endian format) — used with Intel family of microprocessor

An alternate method (i.e., big endian format) is used with theMotorola family of micro-processors



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Word-sized Data

Fig 1.11(a) & (b) shows the weight of each bit position in aword of data



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Example 1.25 shows several signed and unsigned word-sizeddata stored in memory using the assembler program

Note that define word(s) directive or DW causes theassembler to store words in the memory



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Doubleword-sized Data

Doubleword-sized data requires four bytes of memory(32-bit number)

Doubleword-sized data appear as a product after amultiplication and also as a dividend before a division

Fig. 1-12 shows the form used to store doublewords in thememory and the binary weights of each bit position



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To define doubleword-sized data, use assembler

directive define doubleword or DD

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Real Numbers

A real number (floating-point number) contains two parts:a mantissa, significant, or fraction and an exponent

Fig. 1-13 and example 1-27 depicts both the 4-byte (singleprecision) and 8-byte (double precision) forms of real

numbers



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The exponent is stored as a biased exponent

an exponent of 23 is represented as a biased exponent of 127+3or 130 (82H) in the singleprecision form or as 1026 (402H) in thedouble-precision form



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Reference/Text Book

“The Intel Microprocessors”, 8th

Edition, Brey, Barry, B.,Prentice Hall, USA, 2009

3 - assemby language programming for microprocessor

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