ASSEMBLY LANGUAGE

INTRODUCTION

Comment

Part of a program that is ignored by the assembler. It can improve the program's readability and clarity where the purpose of a set of instructions is often ambiguous.

Reserved Words

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

Instructions, Directives, Operators, Predefine Symbols.

Categories of Reserved Words

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. They are not translated into machine language.

Directives

act only during the assembly of a program and generate no machine code.

Operators

Used at assembly time to affect the value of an operand. They don’t correspond to machine instructions.

Pre-defined Symbols

These are 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 reference.

Name and Label.

Types of Identifier

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. Two types are instructions and directives

TITLE

Creates a title up to 60 characters of a source listing.

DOSSEG

Tells the assembler to ignore all other requests 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 stack 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.

Monitor

a typical video screen eighty (80) columns from 0 to 79 and twenty five rows numbered from 0 to 24.

CMP

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

CONDITIONAL JMP

These are instructions that transfer control depending on the setting of CMP instruction whether the condition is met or not.

UNCONDITIONAL JMP

considered an unconditional jump instruction. Does not depend on a condition being true or false.

PROC and ENDP

Every procedure is defined using ___ directives. Making the end and the beginning of a procedure.

STRING INPUT

The following instruction wait for the string, pressing ENTER key.

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 the movement of the printing mechanism or display cursor to the start of next line.

VT (Vertical Tab)

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

FF (Form Feed)

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

CR (Carriage Return)

Indicates the 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.

Direct Console Input without Echo

Waits for the character to be read from the keyboard then returns with the character in AL.

Character Output

Outputs a character to the standard output device.

Character Input with Echo

Waits for a character to be read from the keyboard then echoes it top the screen and return with the character AL.

Get Date

Returns the day of the week, year. month and date

Get time

Returns the time, hours, minutes, seconds and hundredths of seconds.

Program Terminate

Terminates the execution of a program.

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