- 1 Assembly Language
- 2 Design of two Pass Assemblers
- 3 Why do we need a two-pass assembler?
- 4 Difference between One Pass and Two Pass assembler
- 5 C Code For Two Pass Assembler
Assembly Language is a low-level programming language which is used for a computer or other programmable devices. There is a very strong correspondence between the assembly language and the architecture’s machine code instructions.
Every assembly language is system specific i.e, it is unique for every individual system that it operates on which is exactly opposite to
the high-level languages where the language is portable from device to device. but require interpreting or compiling.
Assembly language uses a mnemonic to represent each low-level machine operation or opcode. Some opcodes require one or more OPERANDS as part of the instruction.
Design of two Pass Assemblers
An assembler is a translator, that translates an assembler program into a conventional machine language program. Basically, the assembler goes through the program one line at a time and generates machine code for that instruction. Let us see two pass assemblers
Then the assembler processes to the next instruction. In this way, the entire machine code program is created
What is the difference between one pass and two pass assembler?
What is a single pass assembler?
It is an assembler that generally generates the object code directly in memory for immediate execution.
It parses through your source code only once and you are done.
Now let us see how a two pass assembler works.
Simple, while on its way, if the assembler encounters an
undefined label, it puts it into a symbol table along with the address
where the undefined symbol’s value has to be placed when the symbol is
found in future
Why do we need a two-pass assembler?
As explained, the one-pass assembler cannot resolve forward references of data symbols.
If a data symbol depends on another and this another depends on yet another, the assembler resolved this recursively. If I try explaining even that in this post, the post will become too big. Read this ppt for more details
How does 2 pass assembler work?
2 pass assembler algorithm.
2 pass assembler Design.
2 pass assembler program
Advanced Assembler Directives
- LT ORG
Pass I of the Assembler
Data Structure used in Pass I
Declaration and Assembler Directive Processing
Pass II of the Assembler
- Convert mnemonic operation codes to their machine language equivalents
- Convert symbolic operands to their equivalent machine addresses
- Build the machine instructions in the proper format
- Convert the data constants to internal machine representations
- Write the object program and the assembly listing
Two Pass Assembler
- Read from input line
- LABEL, OPCODE, OPERAND
|Two Pass Assembler|
Design of 2 – Pass Assembler
- Separate the Symbol, Mnemonic opcode, and operand fields
- Build the symbol table
- Perform LC Processing
- Construct Intermediate Representation
Synthesize the target program
ORIGIN < Address Specification>
<Symbol> EQU <Address Specification>E.g. MAXLEN EQU 4096
- Pass I Use following Data Structures
Difference between One Pass and Two Pass assembler
Example Codes of Assemble Code
Example of Assemble Code 2
C Code For Two Pass Assembler
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