Assembly lang

Comment

Part of a program that is ignored by the assembler. It can improve the program readability and clarity

Reserved Words

Words in which the assembler assigns a special meaning and it cannot be used as identifiers

Categories of Reserved Words

Instructions, Directives, Operators, Pre-defined Symbols

Instructions

Statements that will be translated into machine language and executed by the computer

Directives

Statements that give information to the assembler. Also known as pseudo-ops

Directives

These are not translated into machine language but are necessary for the program to assemble properly

Operators

Used at assembly time to affect the value of an operand.

Pre-defined Symbols

Symbols that return information to your program

Identifier

Is a user-defined name or variable that you apply in the program that is used as a reference

Types of Identifier

Name, Label

Name

Refers to the address of a data item

Label

Refers to the address of an instruction or procedure

Statement

It consists of set of statements

Types of statements

Instructions and Directives

TITLE

Creates a title up to 60 characters of a source listing

DOSSEG

Tells the assembler to ignore all other request and adopt the DOS segment sequence-stack, data and code.

MODEL

It specifies and initializes the memory model before defining and segment.

.STACK

Defines the size of the stack. Default size is 1024 bytes

.DATA

Defines and marks the beginning of data segment

.CODE

Defines and marks the code segment which consists of a set of instructions.

.END

Placed at the last line of the source code

String

Used for descriptive data. Ends with $ symbol and defined in “ “

Numeric Constant

Used to define arithmetic values and memory addresses. Defined with a radix specifier such as d for decimal, b for binary, and h for hexadecimal

CMP

Used to compare character data, as well as numeric data fields

JMP

Considered as unconditional jump instruction. Does not depend on a condition being true or false

PROC and ENDP

Every procedure is defined using \___

NUL (Null)

No character. Used for filling in time or filling space on tape when there is no data

BEL (Bell)

Used when there is need to call human attention.

SO (Shift Out)

Indicates that the code combinations shall be interpreted as outside of the standard character set until SHIFT IN character is reached

DEL (Delete)

Used to obliterate unwanted characters

SP (Space)

A nonprinting used to separate words, or to move the printing mechanism or display cursor forward by one position

DLE (Data Link Escape)

A character which shall change the meaning of one or more contiguously following characters.

DLE (Data Link Escape)

Can provide supplementary controls, or permits the sending of data characters having any bit combinations

DC1, DC2, DC3, DC4 (Device Controls)

Character for the control of auxiliary devices or special terminal features

CAN (Cancel)

Indicates that the data which precedes it in message or black should be disregarded.

EM (End of Medium)

Indicates the physical end card, tape or other medium or the end of the required or used portion of the medium

SUB (Substitute)

Substitute for a character that is found to be erroneous or invalid

ESC (Escape)

A character intended to provide code extension in that it gives a specified number of continuously following characters an alternate

BS (Backspace)

Indicates movement of the printing mechanism or display cursor backwards in one position

HT (Horizontal Tab)

Indicates movement of the printing mechanism or display cursor forward to the next pre assigned ‘tab’ or stopping position

LF (Line Feed)

\- Indicates movement of the printing mechanism or display cursor to the start of the next line

VT (Vertical Tab)

\- Indicates movement of the printing mechanism or display cursor to the next of a series of pre-assigned printing lines

FF (Form Feed)

\- Indicates movement of the printing mechanism or display cursor to the starting position of the next page, form or screen

CR (Carriage Return)

\- Indicates movement of the printing mechanism or display cursor to the starting position of the same line

SOH (Start of Heading)

Used to indicate the start of a heading, which may contain address or routing information

STX (Start of Text)

Used to indicate the start of the text and also indicates the end of the heading

ETX (End of Text)

Used to terminate the text, which was started with STX

EOT (End of Transmission)

Indicates the end of a transmission, which included one or more “text’s” with their headings

ENQ (Enquiry)

A request for a response from a remote station.

ACK (Acknowledgement)

A character transmitted by a receiving device as an affirmation response to sender

NAK (Negative Acknowledgement)

A character transmitted by a receiving device as a negative response to polling messages.