Limbaj asamblare emu8086

This tutorial is intended for those who are not familiar with

assembler at all, or have a very distant idea about it. Of course if you

have knowledge of some other programming language (Basic, C/C++,

Pascal...) that may help you a lot.

But even if you are familiar with assembler, it is still a good idea to

look through this document in order to study emu8086 syntax.

It is assumed that you have some knowledge about number

representation (HEX/BIN), if not it is highly recommended to study

Numbering Systems Tutorial before you proceed.

What is an assembly language?

Assembly language is a low level programming language. You need

to get some knowledge about computer structure in order to understand

anything. The simple computer model as I see it:

The system bus (shown in yellow) connects the various

components of a computer.

The CPU is the heart of the computer, most of computations occur

inside the CPU.

RAM is a place to where the programs are loaded in order to be

executed.

Inside the CPU

GENERAL PURPOSE REGISTERS

8086 CPU has 8 general purpose registers, each register has its own

name:

? AX - the accumulator register (divided into AH / AL).

? BX - the base address register (divided into BH / BL).

? CX - the count register (divided into CH / CL).

? DX - the data register (divided into DH / DL).

? SI - source index register.

? DI - destination index register.

? BP - base pointer.

? SP - stack pointer.

Despite the name of a register, it's the programmer who determines

the usage for each general purpose register. The main purpose of a

register is to keep a number (variable). The size of the above registers is

16 bit, it's something like: 0011000000111001b (in binary form), or

12345 in decimal (human) form.

4 general purpose registers (AX, BX, CX, DX) are made of two separate

8 bit registers, for example if AX= 0011000000111001b, then

AH=00110000b and AL=00111001b. Therefore, when you modify any

of the 8 bit registers 16 bit register is also updated, and vice-versa. The

same is for other 3 registers, "H" is for high and "L" is for low part.

Because registers are located inside the CPU, they are much faster

than memory. Accessing a memory location requires the use of a system

bus, so it takes much longer. Accessing data in a register usually takes no

time. Therefore, you should try to keep variables in the registers. Register

sets are very small and most registers have special purposes which limit

their use as variables, but they are still an excellent place to store

temporary data of calculations.

8086 Assembler Tutorial for Beginners