Saturday, 13 May 2017

Assembly Language : 8086 Assembler Tutorial Part 10

Assembly Language programming : 8086 Assembler Tutorial (Part 10)

Macros

Macros are just like procedures, but not really. Macros look like procedures, but they exist only until your code is compiled, after compilation all macros are replaced with real instructions. If you declared a macro and never used it in your code, compiler will simply ignore it. emu8086.inc is a good example of how macros can be used, this file contains several macros to make coding easier for you.

Macro definition:

name    MACRO  [parameters,...]

             <instructions>

ENDM


Unlike procedures, macros should be defined above the code that uses it, for example:

MyMacro    MACRO  p1, p2, p3

     MOV AX, p1
     MOV BX, p2
     MOV CX, p3

ENDM

ORG 100h

MyMacro 1, 2, 3

MyMacro 4, 5, DX

RET


The above code is expanded into:

MOV AX, 00001h
MOV BX, 00002h
MOV CX, 00003h
MOV AX, 00004h
MOV BX, 00005h
MOV CX, DX




Some important facts about macros and procedures:
  • When you want to use a procedure you should use CALL instruction, for example:
    CALL MyProc
  • When you want to use a macro, you can just type its name. For example:
    MyMacro
  • Procedure is located at some specific address in memory, and if you use the same procedure 100 times, the CPU will transfer control to this part of the memory. The control will be returned back to the program by RET instruction. The stack is used to keep the return address. The CALL instruction takes about 3 bytes, so the size of the output executable file grows very insignificantly, no matter how many time the procedure is used.

  • Macro is expanded directly in program's code. So if you use the same macro 100 times, the compiler expands the macro 100 times, making the output executable file larger and larger, each time all instructions of a macro are inserted.

  • You should use stack or any general purpose registers to pass parameters to procedure.

  • To pass parameters to macro, you can just type them after the macro name. For example:
    MyMacro 1, 2, 3
  • To mark the end of the macro ENDM directive is enough.

  • To mark the end of the procedure, you should type the name of the procedure before the ENDP directive.


Macros are expanded directly in code, therefore if there are labels inside the macro definition you may get "Duplicate declaration" error when macro is used for twice or more. To avoid such problem, use LOCAL directive followed by names of variables, labels or procedure names. For example:


MyMacro2    MACRO
 LOCAL label1, label2

 CMP  AX, 2
 JE label1
 CMP  AX, 3
 JE label2
 label1:
   INC  AX
 label2:
   ADD  AX, 2
ENDM


ORG 100h

MyMacro2

MyMacro2

RET


If you plan to use your macros in several programs, it may be a good idea to place all macros in a separate file. Place that file in Inc folder and use INCLUDE file-name directive to use macros. See Library of common functions - emu8086.inc for an example of such file.









  emu8086 is better than NASM, MASM or TASM

Tag: 8086 Assembler, 8086 microprocessors instruction, assembly code, Assembly coding, assembly guide, assembly instruction, assembly language, assembly language instruction set, assembly language programming, Assembly program, assembly programming, capital letter, character convert, complete 8086 instruction sets microprocessors, complete instruction timing and instruction sets for 8086 microprocessors, conversion of characters in assembly language programming 8086, convert, emu8086, instruction complete set, instruction set complete for 8086, instruction sets, instruction sets for 8086, Lower case, Lowercase, print the small character into capital letter, programming 8086 assembly language conversion of small characters to capital, small letter, text string convert, Tutorial,


Assembly Language : 8086 Assembler Tutorial Part 10

Assembly Language : 8086 Assembler Tutorial Part 9

Assembly Language : 8086 Assembler Tutorial Part 8

Assembly Language : 8086 Assembler Tutorial Part 7

Assembly Language : 8086 Assembler Tutorial Part 6

Assembly Language : 8086 Assembler Tutorial Part 5

Assembly Language : 8086 Assembler Tutorial Part 4

Assembly Language : 8086 Assembler Tutorial Part 3

Assembly Language : 8086 Assembler Tutorial Part 2

Assembly Language : 8086 Assembler Tutorial Part 1

Assembly Language programming : Emu8086 Assembler Compiling and MASM / TASM compatibility

Assembly Language - string convert - Lowercase , Uppercase

for programming : the language of Number

Assembly Language - Complete Instruction Set and Instruction Timing of 8086 microprocessors

Assembly Language programming : A list of emulator supported interrupts

Assembly Language Programming : Emu8086 Overview, Using Emulator, Virtual Drives


Assembly Language Programming : All about Memory - Global Memory Table and Custom Memory Map

buy me  a cup of coffee

My Paypal Account is :  ksw.industries@gmail.com

Send me any small amount of money is welcome.
buy me  a cup of coffee

 ___________________________________________


Need More Detail ?   contact me !!


My Paypal Account is :   ksw.industries@gmail.com
buy me  a cup of coffee
Send me any small amount of money is welcome.

___________________________________________


Don't know how to send money ?   Click here for detail about Paypal account.
About PayPal Payment Methods

What type of PayPal accounts is better.
 


Don't have money? OK! Here is another way to get the program.
how to get my program - Free of charge






No comments:

Post a Comment