University:
Mt. San Antonio College
Course:
ELEC 74 | Microprocessor Systems
Academic year:

2024
Views:

55

Pages:

3
Author:

Dipin K.

Assembler Directives of the 8086 Microprocessor Assembler directives are specialized instructions that provide crucial information to the assembler regarding how to process the source code. While they do not directly generate machine code, these directives play a pivotal role in controlling the assembly process. They are indispensable for defining data, segments, and other fundamental aspects of the program. Data Definition Directives DB: Defines bytes of data. DATA DB 20H, 30H, 40H: Defines three bytes of data with values 20H, 30H, and 40H. DW: Defines words (two bytes) of data. NUMBER DW 3234H: Defines a word of data with the value 3234H. DD: Defines double words (four bytes) of data. ADDRESS DD 1200H: Defines a double word of data with the value 1200H. DQ: Defines quadwords (eight bytes) of data. LARGE_NUMBER DQ 12345678H: Defines a quadword of data with the value 12345678H. RESB: Reserves bytes of memory. BUFFER RESB 100: Reserves 100 bytes of memory for a buffer. RESW: Reserves words of memory. TABLE RESW 10: Reserves 10 words of memory for a table. RESD: Reserves double words of memory. ARRAY RESD 5: Reserves 5 double words of memory for an array. RESQ: Reserves quadwords of memory. Segment Definition Directives SEGMENT: Defines the start of a segment. CODE SEGMENT: Defines the start of the code segment. DATA SEGMENT: Defines the start of the data segment. STACK SEGMENT: Defines the start of the stack segment. ENDS: Defines the end of a segment. CODE ENDS: Defines the end of the code segment. DATA ENDS: Defines the end of the data segment. STACK ENDS: Defines the end of the stack segment. Assembly Control Directives ASSUME: Specifies the segment registers to be used for different segments. ASSUME CS: CODE, DS:DATA, SS: STACK: Specifies the code, data, and stack segments. END: Specifies the end of the assembly program. END START: Specifies the end of the program and the starting address. ORG: Sets the origin of the next instruction. ORG 1000H: Sets the origin of the next instruction to memory location 1000H. EQU: Defines an equate. MAX EQU 100: Defines a constant named "MAX" with the value 100. IF, ELSE, ENDIF: Conditional assembly. IF DEFINED MAX: If the symbol "MAX" is defined, assemble the following code. ELSE: Otherwise, assemble this code. ENDIF: End of the conditional assembly. REPEAT, ENDREP: Looping within the assembly. REPEAT 10: Repeat the following code 10 times. ENDREP: End of the loop. Other Directives TITLE: Specifies the title of the program. TITLE GivenPROGRAM: Sets the title of the program to "GivenPROGRAM". PAGE: Specifies the page size and line length. PAGE 60, 80: Sets the page size to 60 lines and the line length to 80 characters. INCLUDE: Includes another source file. INCLUDE THEFILE.ASM: Includes the contents of the file "THEFILE.ASM". EXTERN: Declares external symbols. EXTERN THEFUNCTION: Declares the function "THEFUNCTION" as external. PUBLIC: Declares public symbols. PUBLIC LABEL: Declares the label "LABEL" as public.