Explain the following assembler directives. 1) DB 2) DUP 3) EQU 4) ENDs.

Explain the following assembler directives. 1) DB 2) DUP 3) EQU 4) ENDs.
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1 Answer

Answer :

1) DB (Define Byte or Data Byte):

This is used to define a byte type variable.

The range of values : 0 – 255 for unsigned numbers -128 to 127 for signed numbers

This can be used to define a single byte or multiple bytes

Ex: NUM DB? ; Allocate one memory location

2) DUP (Duplicate memory location):

This directive can be used to generate multiple bytes or words with known as well as un-initialized values.

E.g TABLE DW 100 DUP(0) ; Create array of 100 words all contains data 0

3) EQU (Equate to):

The EQU directive is used to declare the micro symbols to which some constant value is assigned. Micro assembler will replace every occurrence of the symbol in a program by its value.

Syntax: Symbol_name EQU expression

Example: CORRECTION_FACTOR EQU 100

4) ENDs:

This directive informs the assembler the end of the segment

The directives SEGMENT, ENDS are always enclosed in data, code, stack and extra segments.
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