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03 Assembly Programs

Types of Instructions

  1. Data Transfer
  2. Arithmetic
  3. Logical
  4. Branch and Program Control

Steps

  1. initialise segment register
mov ax, 2000h
mov ds, ax

MOV

\[ \textcolor{orange}{ \underbrace{\text{MOV}}_\text{Opcode} } \ \ \textcolor{hotpink}{ \underbrace{\text{dest, src}}_\text{Operands} } \]

Destination/Source could be register/memory location. This is the data, and the operands of the operation

4 bits are required to refer to a register: \(0000-FFFF\)

MOV, ADD, etc… are called mnemonics

\[ \text{MOV dest, src} \]
  • copies contents from src to dest
  • no flags affected
  • size of src and dest must be same; however smaller data can be inserted into bigger register

Possible Options

  • source can be register, memory location, immediate date
  • dest can be register/memory location
From To
Register Memory
Memory Register
Register Register
Index Memory
Index Register

You cannot do MOV [1234] [5678]

INC, DEC

\[ \text{INC dest} \\ \text{DEC dest} \]

increments/decrements the content of the affected register by 1.

inc ax

inc word ptr[bx]
inc byte ptr[bx] ; only low byte

ADD

ADC

First you must use CLC to clear the carry flag.

EQU

used to assign value to a variable. It doesn’t store anything in memory.

count equ 08h
mov cl, count

DUP

Duplicate

array db 5 dup(12h)
array db 5 dup('A')

Flags

Flag Meaning High when
AF Auxiliary internal carry (from lower nibble to higher nibble)
CF Carry carry from the entire byte
OF Overflow overflow
PF Parity even parity (only follows low byte)
SF Sign signed number
ZF Zero data is 0

Branch Instructions

Jump means like go to in C++
JZ Jump on Zero
JNZ Jump on Non-Zero
JE Jump on Equal
JNE Jump on Not Equal
Last Updated: 2023-01-25 ; Contributors: AhmedThahir

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