Assembler

1
Assembler

• A short Overview

2
Content

• Language Levels
• High Level ? micro code
• Machinecode language
• Assembler languages
• Structure
• Commands

3
Language Levels
High Level Language
Assembler Language
Normally deepest free accessible Level
Machine Language
Micro -programming
Firmware
Hardware
4
High Level ? Micro Code

• High Level language
• Formulating program for certain application areas
• Hardware independent
• Assembler languages
• Machine oriented language
• Programs orient on special hardware properties
• More comfortable than machine code
• (e.g. by using symbolic notations)

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High Level ? Micro Code

• Machine code
• Set of commands directly executable via CPU
• Commands in numeric code
• Lowest semantic level
• Generally 2 executing oportunities
• Interpretiv via micro code
• Directly processing via hardware

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High Level ? Micro Code

• Micro programming
• Implementing of executing of machine commands
  (Control unit - controller)
• Machine command executed/shown as sequence of
  micro code commands
• Micro code commands
• Simpliest process controlling
• Moving of data
• Opening of grids
• Tests

7
Machinecode language

• Machinecode command
• Binary word (fix length, causes elementary
  operations within CPU)
• Machinecode program
• sequence of machinecode commands

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Machinecode language

• Structure
• Operationcode
• Defining executable operation
• Operandaddress
• Spezification of operands
• Constants/register addresses/storage addresses
• Difference between 1/2/3 address machines

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Machinecode language

• Data transport commands
• Arithmetic and logical commands
• Process controlling commands
• In-/output commands
• Special commands
• Disadvantage
• Difficultly readable
• No symbolic names(Mnemomics)

10
Assembler languages

• Translated into machinecode language(Interpreter)
• Each operation code(opcode) owns one symbolic
  command
• Assignments of operand addresses are possible
• Labels for command addresses

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Assembler languages

• Usage of pseudo commands
• Commands for assembler
• Assigment of values/addresses(variables)
• Definition of the programstart addresses
• Allocating of memory for variables

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Assembler languages-structure

• Label
• symbolic labeling of an assembler address
  (command address at Machine level)
• Mnemomic
• Symbolic description of an operation
• Operands
• Contains of variables or addresse if necessary
• Comments

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Assembler Languages - Machine Instructions

• Bitpatterns are created, executed as commands by
  CPU
• Classes
• Arithmetic/logical Operations(ADD,SUB,XOR,
  administrative commands - EQU, shiftingrotation
  commands)
• Data transfer(load/save operations,
  speicherltgtregister, registerltgtregister)
• Control commands(jump op. un-conditional
  /relativ,control op. STOP)
• In-/output commands

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Assembler Assembler Instructiuons (Pseudo
Commands)

• Instructions to assembler
• Controlling translation process
• No creation of machine code
• Affect creation of machine instructions
• Types
• Program organisation
• equations and symbolic Addresses
• Definition of Constants and Memory
• Addressing

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Assembler All purpose Register

• Arithmetic example
• Source and Destination Data width has to euqal
• AX , BX, CX, DX, SI, DI, BP, SP
• arithmetic operations
• ADD AX, BX AX AXBX
• SUB AH,AL AH AH - AL
• MOV AL, CL AL CL
• INC CX CX CX1
• DEC CL CL CL-1
• NEG CX CX -CX

All purpose Register
AX
BX
CX
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Assembler Special Register

• Unless to all-purpose registers
• Special register(SS, DS, CS, ES, IP)
• Never ever are
• Destination/Source of a mov command
• Destination of arithmetic operations

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Assembler Flag Register
Zero
Carry
Sign
Parity
Trap
Auxiliary carry
Interrupt enable
Direction
Overflow
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Assembler Flag Register

• FLAG-Bits
• C Carry Area crossing of unsigned numbers
• A Aux. Carry Area crossing at BCD-design
• O Overflow Area crossing at arithmetic
  operation with signed numbers
• S Sign True if result negativ
• Z Zero Result Null
• P Parity Result has an even number of 1 Bits
• D Direction flag Defines direction of
  string- commands
• I Interrupt Global Interrupt Enable/Disable Flag
• T Trap Flag Used by debugger, allows
  single-step- modus

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Assembler Flag Register

• Missing flags
• V Twos complement overflow indicator
• H Half Carry Flag
• Operations and flags
• ADD, SUB, NEG affects O, S, Z, A, P, C
• INC, DEC -- O, S, Z, A, P
• MUL, DIV -- O, C
• AND, OR , XOR -- S, Z, P, C

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Assembler Jump Operations

• Un-/conditioned jumps
• Example
• Mov AX, 0
• CMP CX, 0
• again JZ end (jumpzero, conditioned j.)
• ADD AX, CX
• DEC CX
• JMP again (unconditioned jumped)
• end NOP

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Sources

• http//www.informatik.ku-eichstaett.de
  /studium/skripte/ws0203/einf2/Vorlesung12.ppt
• http//www-ist.massey.ac.nz
• /GMoretti/159704/Lectures/1-Languages-Translation-
  -Assemblers.pdf
• http//www.mathematik.uni-marburg.de
• /priebe/lehre/ws0001/ti1/Skript/TechInf1Lo08.ppt
• E\temp\4.Semester\Intro into Dig.Computing\Doku\B
  efehlssatz.pdf

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Thanks 4 ur Attention

• Any further
• questions
• ??