Assemblers
Prepared By: Dr. D. P. Singh
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Assembler: Role in Translating Source Code to Object Code, Summaries of Systems Design
An overview of the role of an assembler in translating mnemonic language code to its equivalent object code. It explains the basic features of an assembler, the functions it performs during the translation process, and the use of assembler directives. The document also includes examples of object codes and their corresponding source codes.
What you will learn
- What are assembler directives and how are they used?
- What are the basic features of an assembler?
- How does an assembler translate symbolic operands to their equivalent machine addresses?
Typology: Summaries
2021/2022
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Assemblers
Prepared By: Dr. D. P. Singh
Basic Assembler Features
Assembler Object Program
- Translating mnemonic language code to its equivalent object code.
- Assigning machine addresses to symbolic labels.
Source Program
Simple SIC Assembler
The translation of source program to object code requires to
accomplish the following functions
- Convert mnemonic operation codes to their machine language
equivalents
- Convert symbolic operands to their equivalent machine addresses
- Decide the proper instruction format
- Convert the data constants to internal machine representations
- Write the object program and the assembly listing
All of these functions except 2 can easily be accomplished by
sequential processing of the source program one line at a time
Forward Referencing
PROG START 1000
1000 LDA FIVE
1003 STA ALPHA
1006 LDCH CHARZ
1009 STCH C
100C ALPHA RESW 1
100F FIVE WORD 5
1012 CHARZ BYTE C’Z’
1013 C1 RESB 1
END
Because of Forwarding Referencing
most assemblers make two passes over
the source program
First pass: scan the source program for
label definitions and assign addresses
Second pass: perform actual
translation
In addition to translating the instructions of the source
program, assembler must process the assembler
directives.
Finding Object Codes cntd…
Example 2
PROG2 START 0
0000 LDT(74) #11 75000B
0003 LDX(04) #0 050000
0006 MOVECH LDCH(50) STR1,X 53A
0009 STCH(54) STR2,X 5 7A
000C TIXR(B8) T B
000E JLT(38) MOVECH 3B2FF
0011 STR1 BYTE C’TEST STRING’ 54455354205
35452494E
001C STR2 RESB 11
END
disp= TA- (PC)
disp= TA- (PC)
=001C-000C=
disp=TA-(PC)
=-000B
2’s complement
= FF
Size of the Program=0027-0000=0027(in Hex)
Thank You