assembler shqip

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Assembler design


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Hypothetical machineProcessor architecture

Main

memory

Simplified

Instructional

Computer(SIC)Size=6!"

Memory Address=# "ytes


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$ord lengthAccumulator%&egisters '%

Main Memory

*

6

+

,#

* "ytes"yte "yte "yte

"yte "yte "yte

Address-

# bytes


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Instruction set

of SIC


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Instruction format

.p code (, byte) Address (# bytes)


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Sample code (data mo/ement)

01S0 S0A&0 ,*

2I&S0 3A 2I41

S0A AP5AAP5A &1S$ , 7symbolic /ariable7

2I41 $.&3 8 7symbolic constant% iteral 7

193 2I&S0

LABEL Instruction Operand

Assembly language program

Psuedo Opcode ORAssembler Directives

S0A&0

&1S$

$.&3%

193


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01S0 S0A&0 ,*

2I&S0 3A 2I41 ,,#

S0A AP5A C,+

AP5A &1S$ , 777777

2I41 $.&3 8 8

193 2I&S0

,*

,6,+

,,#

,,8

Sample code (data mo/ement)oc LABEL Instruction Operand Object code



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Sample code (Arithmetic

operation)3A AP5A

A33 I9C&

S:" .91

S0A "10A

.91 $.&3 ,

AP5A &1S$ ,"10A &1S$ ,

I9C& &1S$ ,


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Assembler

AssemblerAssembly language

code

.b;ect code


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01S0 S0A&0 ,*

2I&S0 3A 2I41 ,,#

S0A AP5A C,+AP5A &1S$ , 777777

2I41 $.&3 8 8

193 2I&S0

,*

,*

,6,+

,,#

,,*




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5o< to design an Assembler

3ata structures

Instruction

Op code Lengthbytes!

A33 m , *

3A m *

"! OP#AB

LABEL Address LO$value!

2I&S0 ,*

AP5A ,+

2I41 ,,#

%! &ymbol #able

'! Location counter LO$!

I i O d L h


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3ata Structures

> .peration Code 0able (.P0A")

?:sed to loo@ up mnemonic operation codes and

translate them into machine languageeui/alents

?Contains the mnemonic operation code and its

machine language eui/alent

?In more compleB assemblers% contains

information li@e instruction format and length

Instruction

Op code Lengthbytes!

A33 m , *

3A m *


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3ata Structures

> Symbol 0able

?:sed to store /alues (addresses) assigned to

labels?Includes the name and /alue for each label

?2lags to indicate error conditions% eg duplicate

definition of labels?May contain other info li@e type or length about

the data area or instruction labeled

LABEL Address LO$value!

2I&S0 ,*

AP5A ,+

2I41 ,,#


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3ata Structures

> .CC0&

?:sed to help in the assignment of addresses

?Initialized to the beginning address specified in

the S0A&0 statement

?After each source statement is processed% the

length of the assembled instruction or data areato be generated is added

?Di/es the address of a label


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0


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0


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01S0 S0A&0 ,*

2I&S0 3A 2I41 ,,#

S0A AP5A C,+AP5A &1S$ , 777777

2I41 $.&3 8 8

193 2I&S0

,*

,*

,6,+

,,#

,,*




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5 E C.PF E , E ,GA

0 E , E ,1 E ,,** E #*+ E ,*6 E H

0 E ,,1 E ,8 E C,*6 E #6, E ,** E H

H

0 E #G* E G E *#6 E C E 8

1 E ,

5eader record-

Col , 5

Col #G Program name

Col ,* Starting address of ob;ect program (heBadecimal)

Col ,,+ ength of ob;ect program in bytes (heBadecimal)

0eBt record-Col , 0

Col #G Starting address for ob;ect code in this record (heBadecimal)

Col + ength of ob;ect code in this record in bytes (heBadecimal)

Col , ? 6+ .b;ect code% represented in heBadecimal (6+,J,)6=, instructions

1nd record-

Col , 1

Col #G Address of first eBecutable instruction in ob;ect program (heBadecimal)


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begin

read first input line

if .PC.31 = KS0A&0K then

begin

sa/e L.P1&A93N as starting address

initialized .CC0& to starting address


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begin

read first input file Ofrom intermediate file

if .PC.31 = KS0A&0K then

begin


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5 E C.PF E , E ,GA

0 E , E ,1 E ,,** E #*+ E ,*6 E H

0 E ,,1 E ,8 E C,*6 E #6, E ,** E H

H

0 E #G* E G E *#6 E C E 8

1 E ,

5eader record-

Col , 5

Col #G Program name

Col ,* Starting address of ob;ect program (heBadecimal)

Col ,,+ ength of ob;ect program in bytes (heBadecimal)

0eBt record-Col , 0

Col #G Starting address for ob;ect code in this record (heBadecimal)

Col + ength of ob;ect code in this record in bytes (heBadecimal)

Col , ? 6+ .b;ect code% represented in heBadecimal (6+,J,)6=, instructions

1nd record-

Col , 1

Col #G Address of first eBecutable instruction in ob;ect program (heBadecimal)

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