1. Assembler
A short Overview
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2. Content
 Language Levels
 High Level  micro code
 Machinecode language
 Assembler languages
 Structure
 Commands
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3. Language Levels
High Level Language
Assembler Language
Machine Language Normally deepest free
accessible Level
Micro „Firmware“
-programming
Hardware
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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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5. 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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6. 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
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• 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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8. Machinecode language
 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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9. Machinecode language
 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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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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11. 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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12. 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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13. 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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14. 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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15. 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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16. 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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17. 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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18. 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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19. Assembler – Flag Register
 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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20. 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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21. 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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22. Thanks 4 ur Attention
Any further
questions
??
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