Assembly Basics

Introduction

This article gives details about assembly programming for the Intel 8086 microprocessor. It also presents very clear details by providing example cases, definitions and syntax explanations on arithmetic instructions, logical instructions and operands.

Why study this topic? It’s important to understand the basic concepts of computer architecture, chip logic and memory management. People dealing with malware will also find it useful. Irrespective of the type of high-level language being used, before the code gets translated to machine code, it first must be translated into assembly language. This makes assembly language still important despite the evolution of high-level languages.

Assembly language

An assembly language is a low-level programming language designed for a specific type of hardware processor. This low-level language is developed using mnemonics. Prior to writing a program in assembly language, it is necessary to have sufficient knowledge of the hardware for the controller or processor. 

Figure 1

Figure 2

The 8086 processor architecture 

As discussed on Elprocus, the architecture for the 8086 microprocessor is based on complex instruction set computing (CISC). This means the microprocessor has the capacity to perform multi-step operations or addressing modes within one instruction set. CISC is a CPU design where one instruction works several low-level acts such as memory storage, loading from memory and an arithmetic operation. 

Registers

So that it can store information (under different values and different sizes), each processor is composed of different parts, “boxes,” called registers.

Syntax

LABEL: INSTRUCTION ; COMMENT

The label is just an address identifier

Labels

A label can be placed at the beginning of a statement. During assembly, the label is assigned the current value of the active location counter and serves as an instruction operand.

Comments begin with a semicolon (;) and do not generate machine codes. In other words, they (Read more...)