Assembly Language

1
Assembly Language

• Chapter 1

2
Basic Concepts

• Assembly Language is the oldest programming
  language
• Bears closest resemblance to the native language
  of a computer
• Provides direct access to a computers hardware
• Thus, you have to understand a great deal about
  the computers architecture and OS

3
Basic Concepts 1.1.1 Questions

• What background should I have?
• C, C, Java, or Visual Basic.
• What is an assembler?
• A program that converts source-code programs from
  assembly into machine language
• A companion program, called a linker, combines
  individual files created by the assembler.
• A third program called a debugger allows a
  programmer to trace the execution of a program
• Most popular assemblers are TASM by Borland and
  MASM by Microsoft

4
Basic Concepts 1.1.1 Questions

• What hardware and software do I need?
• Editor simple text editor to create the
  assembly language code such as TextPad by Helios
  Software supplied in the CD-ROM or NotePad or the
  MS VS editor
• Assembler --- MASM (6.15) supplied in the CD-ROM
  or TASM (by Borland)
• Linker Two linkers are supplied LINK.EXE (16
  bit) or LINK32.EXE (32 bit)
• Debugger For MS-DOS programs, MASM supplies a
  good 16-bit debugger called CodeView. Or MS
  (msdev.exe)

5
Basic Concepts 1.1.1 Questions

• What types of programs will I create?
• 16-Bit Real Address Mode If your running pure
  MS-DOS or a DOS emulator, you can create 16-bit
  Real address mode programs.
• 32-Bit Protected Mode If your using Microsoft
  Windows, you can create 32-bit Protected mode
  programs that display both text and graphics

6
Basic Concepts 1.1.1 Questions

• How does assembly language relate to machine
  language?
• First, machine language is a numeric language
  that is specifically understood by a computers
  processor (the CPU). Intel processors for
  example, have a machine language that is
  automatically understood by other Intel
  processors. Machine language consists purely of
  numbers
• Assembly Language --- consists of statements that
  use short mnemonics such as ADD, MOV, SUB, and
  CALL. An Assembly language instruction has a
  one-to-one relationship with a machine language
  instruction

7
Basic Concepts 1.1.1

• How do C and Java relate to assembly language?
• High-level languages such as C and Java have a
  one-to-many relationship with both assembly
  language and machine language. A single
  statement in C, for example, expands into
  multiple assembly language or machine
  instructions.

8
Basic Concepts Example one to many
relationship

• C code example
• X (Y 4 ) 3
• Turns into .
• mov eax, Y
• add eax, 4
• mov ebx, 3
• imul ebx
• mov X, eax

9
Basic Concepts

• Is Assembly Language portable?
• Assembly language instructions are tied to a
  specific processor thus it makes no attempt to be
  portable
• Why learn assembly language?
• Working towards a degree in computer engineering
• May be a dedicated game programmer with stringent
  memory restrictions
• Help you gain an overall understanding of
  interactions between computer hardware , OS and
  application prog
• Working as a hardware manufacture to create
  device drivers

10
Chapter 1.3

• Binary Numbers
• A computer stores instructions and data in memory
  as collections of electronic charges
• 1 for on or True 0 for off or False
• Binary numbers are base 2 numbers each binary
  digit called a bit (either 0 or 1)
• Bits are numbered at zero on the right side,
  increasing towards the left
• The bit on the left is called the Most
  Significant bit (MSB)
• The bit on the right is called the Least
  Significant Bit (LSB)

11
Chapter 1.3

• Unsigned Binary Integers
• 1 1 1 1 1 1
  1 1
• 27 26 2 5 24 23 22 21
  20
• Translating Unsigned Binary to Decimal
• Dec (Dn-1 X 2n-1) (D1 X 21) (D0 X 20)
• Short cut (exp) or Double dabble method

12
Chapter 1.3

• Translating Unsigned Decimal Integers to Binary
• Repeatedly divide the decimal value by 2, saving
  each remainder as a binary digit.
• The first remainder is D0 then D1, D2, D3 so on

13
Chapter 1.3.2

• Binary Addition
• 0 0 0
• 0 1 1
• 1 0 1
• 1 1 1 0

14
Chapter 1.3.3

• Integer Storage Sizes
• Basic storage Size in IA-32 based computer is a
  byte, containing 8 bits
• Other storage sizes
• Word (2 bytes) 16 bits
• Doubleword (4 bytes) 32 bits
• Quadword (8 bytes) 64 bits

15
Chapter 1.3.4 Hexadecimal Integer

• Large binary numbers are cumbersome to read, so
  hexadecimal digits are usually used by assemblers
  and debuggers to represent binary data.
• Each digit in a hexadecimal integer represents
  four binary bits and two hexadecimal digits
  together represent a byte.

16
Chapter 1.3.4 Hexadecimal Integers

• A single hexadecimal digit can have a value from
  0 to 15, so the letters A to F are used, as well
  as the digits 0-9
• The letter A10, B11, C12, D13, E14, and F
  15.
• Example
• 0001 0110 1010 0111 1001 0100
• 1 6 A 7 9 4

17
Chapter 1.3.4.1 Converting Unsigned Hexadecimal
to Decimal

• In hexadecimal, each digit position represents a
  power of 16. For example in a 4-digit hexadecimal
  integer
• Dec(D3 X 163) (D2 X 162) (D1 X 161)
  (D0 X 160)
• Example 3BA4 15,268

18
Chapter 1.3.4.2 Converting Unsigned Decimal to
Hexadecimal

• To convert an unsigned decimal integer to
  hexadecimal
• Repeatedly divide the decimal value by 16, and
  keep each remainder as a hexadecimal digit.
• Example 422 to hexadecimal
• Turns into 1A6 collecting the digits in reverse
  order. Last Reminder goes first and so on

19
Chapter 1.3.5 Signed Integers

• Signed binary integers can be either positive or
  negative.
• In general, the most significant bit (MSB)
  indicates the numbers sign.
• A value of 0 indicates that the integer is
  positive, and 1 indicates that it is negative

20
1.3.5.1 Twos Complement Notation

• Negative integers are represented using what is
  called twos complement representation.
• The twos complement of an integer is simply its
  additive inverse.
• The twos complement of a binary integer is found
  by reversing its bits and adding 1.
• Twos complement representation is useful to
  processor designers because it removes the need
  for separate digital circuits to handle both
  addition and subtraction.
• For example if faced with the expression A-B, the
  processor can simply convert it to an addition
  expression A (-B)