ASSEMBLER DIRECTIVES OF 80386 PDF

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.

The logical errors or other programming errors are not found by the assembler. For completing all these tasks, an assembler needs some hints from the programmer. These types of hints are given to the assembler using some predefined alphabetical strings dierctives assembler directives, which helps the assembler to correctly understand the assembly language program to prepare the codes.

Another type of hint which helps the assembler to assign a particular constant with a label or initialize particular memory locations or labels with constants is an operator. The DB directive is used to reserve byte or bytes of memory locations in the available memory. The DW directive serves the same purposes as sasembler DB directive, but it makes the assembler reserves the number of memory words 16bit instead of bytes.

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. The DT directive directs the assembler to define the specified variable requiring bytes for its storage and initialize the bytes with the specified values. Assume Logical Segment Name: 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.

The END directive marks the end of an assembly language program.

The ENDP directive is used to indicate the end of a procedure. This directive marks the end of a logical segment. Align On Even Memory Address: The EVEN directive updates the location counter to the next even address, if the current location counter contents are not even, and assigns the following routine or variable or constant to that address. If the content of the location counter is already even, then the procedure will be assigned with the same address. The directive EQU is used to assign a label with a value or symbol.

Write short notes on assembler directives

The use of this directive is just to reduce the recurrence of the numerical values or constants in the program code. The directive EXTERN informs the assembler that the names, procedures and labels declared after this directive have already been defined in some other assembly language module. Group the Related Segments: This directive is used to form logical groups of segments with similar purpose or type. The label directive can be used to refer to the data segment along with the data type, byte or word.

Byte Length Of A Label: This directive is used to refer to the length of a data array or assembker string. Not available in MASM. The label, variables, constants or procedures declared LOCAL in a module are to be used only by that particular module.

Logical Name Of A Module: The NAME directive is used to assign a name to an assembly language program module. Offset Of A Label: 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. The PROC directive marks the start of a named procedure in the statement. The started segment is also assigned a name, i. The SHORT operator indicates the assembler that only one byte is required to code the displacement for a jump.

This method of specifying jump address saves memory. These operators represent arithmetic addition and subtraction respectively. And are typically used to add or subtract displacements 8 or 16 bit to base or index registers or stack or base pointers. This directive indicates the assembler that the label following FAR PTR is not available within the same segment and the address of the bit is of 32 bits i.

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Newer Post Older Post Home. Popular Tags Blog Archives. Like Us On FaceBook! For completing all these tasks, an assembler needs some IR0 has the highest priority and IR7 has the lowest one.

Macro Assembler Directives

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