Assembler directives of 8086 microprocessor

RodolfoNeres via Wikimedia Commons Writing assembly language is something best left for the experts. To write code that runs directly on your microprocessor you need to know how memory segmentation works, what the intended use of each register is, how codes executes in real and protected modes and much, much more.

Assembler directives of 8086 microprocessor

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The ASSUME directive tells the assembler to assume, that a certain register contains the base of some structure in your case: In your case, CS and DS point to the code segment and the data segment respectively, both the one and only of their respective kind.

So CS is already assumed as a pointer to the code segment, because the code segment is the only one. If you would change, for example, DS with mov ax, h ; mov ds, ax to a hypothetical second data segment located at segment address h, some references to the content can be mislead.

The follwing code snippets are not correct and would not assemble, their sole purpose is to illustrate the difference!

Assembler directives of 8086 microprocessor

Why is this so? So the index of the variable multiplier is 2 instead of 0 and therefore the value is accessed at the wrong place. Hence the different result. An inappropriate application of the assume directive can create hard-to-detect bugs.

BTW, the assume directive can be used for convenience purposes like generalizing the access to structures in registers which will increase the readability of code: Welcome to Stack Overflow!Advanced Microprocessor Assembly Programs Instruction Formats in Microprocessor instructions for the The assembler directives described here are those for the Intel macro-assembler (ASM86), the Borland Turbo Assembler (TASM), Documents Similar To advanced microprocessors Interrupt Structure of 5/5(4).

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Assembler Directives & Macros Introduction To Segmentation: The microprocessor has 20 bit address pins; these are capable of addressing 1MegaByte memory. To generate this 20 bit physical address from 2 sixteen bit registers, the following procedure is adopted.

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Assembler Directives of Microprocessor - Instruction Set and Assembly Language, Objective type Questions, mock tests for examination, past year papers, Viva Questions, Sample Paper, Extra Questions, Semester Notes, Important questions, study material, video lectures. Writing assembly language is something best left for the experts.

To write code that runs directly on your microprocessor you need to know how memory segmentation works, what the intended use of each register is, how codes executes in real and protected modes and much, much more.

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