Assembler

Assembler

A short Overview

1

Content

 Language Levels
 High Level  micro code
 Machinecode language

 Assembler languages
 Structure
 Commands

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Language Levels
High Level Language

Assembler Language

Machine Language Normally deepest free
accessible Level

Micro „Firmware“
-programming

Hardware
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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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 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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 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
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• Tests

Machinecode language

 Machinecode command:
 Binary word (fix length, causes
elementary operations within CPU)

 Machinecode program
 sequence of machinecode commands

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 Structure: OpCode OpAddress

 Operationcode
• Defining executable operation
 Operandaddress
• Spezification of operands
• Constants/register addresses/storage
addresses
 Difference between 1/2/3 address
machines
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 Data transport commands
 Arithmetic and logical commands

 Process controlling commands

 In-/output commands

 Special commands

 Disadvantage:
 Difficultly readable
 No symbolic names(Mnemomics)
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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> <Mnemomic> <Operand> Comments
 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,
shifting&rotation commands)
 Data transfer(load/save operations,
speicher<>register, register<>register)
 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
All purpose
ADD AX, BX ; AX := AX+BX Register
SUB AH,AL ; AH := AH - AL
MOV AL, CL ; AL := CL AX AH AL
INC CX ; CX := CX+1
DEC CL ; CL := CL-1 BX BH BL
NEG CX ; CX := -CX
CX CH CL

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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

O D I T S Z A P C

Zero
Sign Carry
Trap Parity
Interrupt enable Auxiliary carry
Direction

Overflow
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 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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 Missing flags:
• V: Two’s 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:temp4.SemesterIntro into Dig.ComputingDokuBefehlssatz.pdf

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Thanks 4 ur Attention

Any further
questions
??

22

Assembler

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Assembler