Introduction To Segmentation: The microprocessor has 20 bit address pins; these are capable of addressing 1MegaByte memory. Causes all segments to default to DWORD alignmentP enabled assembly of all instructions (see) enabled assembly of instructions . This directive tells the assembler the name of the logical segment it should use for a specified segment. For example ASSUME CS:CODE, tells.

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Asaembler Also called as pseudo operations that control the assembly process. EVEN This directive instructs the assembler to increment the location of the counter to the next even address if it is not already in the even address. Executable statements- These are the statements to be executed by the processor.

When EVEN is used the location counter will simply incremented to next address and NOP instruction is inserted in that incremented location. The ASSUME directive is used to inform the assembler, the names of the logical segments to be assumed for different segments used in the program. For example, if you want to call a procedure, which in assemmbler program module assembled at a different time from that which contains the CALL instruction, you must tell the assembler that the procedure is external.

Same is the case with stack and extra segments also, which are only different type of data storage facilities. MODEL- This directive is used for selecting a standard memory model for the assembly language program.

This directive is used to direct the assembler to reserve 4 words 8bytes of memory for the specified variable and may initialize it with the specified values. DQ — Define Quadword. When all the modules are working correctly, their object code files are linked together to form the complete program. But leave the bytes un-initialized. It is the task dirdctives the assembler designer to select the suitable strings for using them as directives,pseudo operands or reserved words and decides syntax.


This is because the END directive terminates the entire program. Loader linker further converts the object module prepared by the assembler into executable form, assemblfr linking it with other object modules and library modules.

This directive is used to refer to the length of a data array or a string. A carriage return is required after the END directive. This directive is used to define a variable of type doubleword or to reserve storage location of asssembler doubleword in memory.

END- This is placed at the end of a source and it acts as the last statement of a program. The assembler directives can be divided into two categories namely the general purpose directives and the special directives.


Assembly language consists of two types of statements viz. The PROC directive marks the start of a named procedure in the statement. This is called the base address. Offset Of A Label: Byte Length Of A Label: The contents of the segment registers are shifted left four times with zeroes 0? The ORG directive directs the assembler to start the memory allotment for the particular segment, block or code from the declared address in the ORG statement. Generally, the program does not know the exact physical address of an instruction.

The final executable map of the assembly language program is prepared by the loader at the time of loading into the primary memory for actual execution. DD — Define Doubleword.

It will initialize the 10 bytes with the values 11, 22, 33, 44, 55, 66, 77, 88, 99, and 00 when the program is loaded into memory to be run.

You get question papers, syllabus, subject analysis, answers – all in one app. The directive EQU is used to assign a label with a value or symbol. This method of specifying jump address saves memory.

Define Ten bytes [DT]- It is used to define the data items that are 10 bytes long.


If the word starts at an odd address, the will take 2 bus cycles to get the data. DB — Define Byte This directive is used to declare a byte type variable or to store a byte in memory location. Define Double word [DD]- It defines the data items that are a double word four bytes in length.

Each module is individually assembled, tested, and debugged. Rest will be added with time…….

Macro Assembler Directives

So in order to test the program with a different set of data, one need not change the program but only have to alter the data. The PUBLIC directive is used to tell the assembler that a specified name or label will be accessed from other modules. DT — Define Ten Bytes This directive is used to define or variable which is 10 bytes in length or to reserve 10 bytes of storage in the memory.

The works directly with only 4 physical segments: This directive is used to define a variable of type word or to reserve storage location of type word in memory. These types of hints are given to the assembler using some predefined alphabetical strings called assembler directives, which helps the assembler to correctly understand the assembly language program to prepare the codes.

In many cases the program is optimized and kept unaltered for the specific application. Procedure for assembling a directievs Assembling a program proceeds statement by statement sequentially.

They indicate how an operand or section of a program to be processed by the assembler. Popular Tags Blog Archives.