JNTU B.Tech III MICROPROCESSORS AND MICROCONTROLLERS Previous Question Paper (November/December - 2020 - R16)

Assembler directives are commands provided to the assembler that control the assembly process, memory allocation, and program structure. They do not generate machine code but provide instructions to the assembler regarding how to translate the assembly language source code into object code.

Common 8086 assembler directives include:

• DB (Define Byte): Allocates one or more bytes of memory for variables.
• DW (Define Word): Allocates one or more 16-bit words of memory.
• DD (Define Double Word): Allocates 32 bits of memory for double-word variables.
• EQU (Equate): Assigns a specific value or expression to a label, which cannot be redefined later.
• ORG (Origin): Sets the starting address for the program or data segment in memory.
• ASSUME: Informs the assembler which segment register is associated with which segment name.
• PROC/ENDP: Defines the beginning and end of a procedure.
• END: Marks the physical end of the source program.

The following assembly language program finds the largest number in an 8-bit array stored in memory:

DATA SEGMENT
ARRAY DB 12H, 45H, 09H, 88H, 32H
COUNT EQU 05H
RESULT DB ?
DATA ENDS

CODE SEGMENT
ASSUME CS:CODE, DS:DATA
START: MOV AX, DATA
MOV DS, AX
LEA SI, ARRAY
MOV CX, COUNT
MOV AL, [SI]
DEC CX
INC SI

LOOP1: CMP AL, [SI]
JNC NEXT
MOV AL, [SI]
NEXT: INC SI
LOOP LOOP1
MOV RESULT, AL
MOV AH, 4CH
INT 21H
CODE ENDS
END START