Assembly Language Week 10 ' Modular programming and Macro '

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Assembly LanguageWeek 10 .Modular
programming and Macro .
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Modular program

• Assembly Programming can use Modular
• Design which can help to develop a big
• program because it will separate into many
• part of procedure in many file that can link
• all together in the final.
• By using EXTRN and PUBLIC command

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How to use EXTRN and PUBLIC
Must Call P1 from other file
MAIN.ASM
P1.ASM
CODE SEGMENT ASSUME CSCODE MAIN PROC
FAR EXTRN P1FAR . . CALL P1 CALL
TERMINATE MAIN ENDP TERMINATE PROC
MOV AX,04C00H INT 21H TERMINATE
ENDP CODE ENDS END MAIN
CODE SEGMENT PUBLIC P1 ASSUME
CSCODE P1 PROC FAR . . . RET P1
ENDP CODE ENDS END P1
P1 in this file is public.
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How to Compile EXTRN and PUBLIC
Compile each ASM with TASM to get OBJ files
C\gtTASM MAIN.ASM C\gtTASM P1.ASM C\gtLINK
MAIN.OBJ P1.OBJ C\gtMAIN.EXE
Link all OBJ files together by LINK xx.obj
xx.obj ...
RUN
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Example of EXTRN and PUBLIC
STSEG SEGMENT STACK DB 64 DUP(?) STSEG
ENDS CODE SEGMENT ASSUME
CSCODE,SSSTSEG MAIN PROC FAR EXTRN
DISPBINFAR SUB AL,AL AGAIN PUSH AX
CALL DISPBIN MOV DL,20H
MOV AH,2 INT 21H MOV AH,2 INT
21H POP AX INC AL JNZ
AGAIN CALL TERMINATE MAIN
ENDP TERMINATE PROC MOV AX,04C00H
INT 21H TERMINATE ENDP CODE ENDS END MAIN
TESTBIN.ASM
"TESTBIN.ASM" is the program to print set of
BINARY number. This program cooperation with
DISPBIN.ASM Follow this to Run
this program C\gtTASM TESTBIN.ASM
C\gtTASM DISPBIN.ASM
C\gtLINK TESTBIN.OBJ
DISPBIN.OBJ C\gtTESTBIN.EXE
Call DISPBIN from other file
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Example of EXTRN and PUBLIC (cont.)
CODE SEGMENT PUBLIC DISPBIN
ASSUME CSCODE DISPBIN PROC FAR MOV
CX,8 NEXT SHL AL,1 PUSH AX
JC ITIS1 MOV DL,30H JMP
SAY01 ITIS1 MOV DL,'1' SAY01 MOV AH,2
INT 21H POP AX LOOP NEXT
RET DISPBIN ENDP CODE ENDS END
DISPBIN
DISPBIN.ASM
"DISPBIN.ASM" is the program to print set of
BINARY number. This program cooperation with
TESTBIN.ASM Follow this to Run this
program C\gtTASM TESTBIN.ASM
C\gtTASM DISPBIN.ASM
C\gtLINK TESTBIN.OBJ
DISPBIN.OBJ
C\gtTESTBIN.EXE

DISPBIN is public procedure
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Macro

• Macro is a set of assembly language statements
  given a symbolic name.
• Macro is invoked, not called. A copy of the macro
  is inserted directly into the program
• After being defined, the assembler will
  substitute those statements whenever it finds the
  symbolic name

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Example of Macro

• Lets define macros to input and print a
  character
• mInputChar macro mov ah, 1 int
  21hendmmPutChar macro mov ah, 2 int
  21hendm

Macro for get input a character and store in AL
Macro for print a character in dl to screen
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Example of Macro (cont.)

• Code segment
• .
• .
• mInputCharmov dl, almPutChar
• .
• .
• Code ends
• End start

Results in the code . . mov ah,
1 int 21h mov dl, al mov ah, 2
int 21h Observe the text substitution
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Macro with parameter

• Macros can have parameters. The text for the
  actual parameter is substituted for the name of
  the dummy parameter when the macro is invoked.

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Example of Macro with parameter

• mInputChar macro aChar push ax mov ah,
  1 int 21h mov aChar, al pop ax
• endm

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Example of Macro with parameter (cont.)

• Code segment
• .
• .
• mInputChar blmInputChar aCh
• .
• .
• Code ends
• End start

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Example of Macro with parameter

• This macro is used to create a buffer
• for function 0Ah, int 21h
• mInputBuf macro len InBuf label byte
  MaxLen db len InLen db ? Buf
  db len dup (?) endm
• Then mInputBuf 20
• expands to InBuf label byte MaxLen db
  20 InLen db ? Buf db 20 dup (?)

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Macros vs. Procedures

• Similarities Both
• Simplify program writing
• Encourage reuse of code
• Improve program readability
• Provide better structure to programs

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Macros vs. Procedures (cont.)

• Differences

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Macros vs. Procedures (cont.)

• Use macros for short code segments, procedures
  for longer ones.

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Local Label

• 8088 lacks a "near" jump loop instruction. Lets
  try to create it.
• mNearLoop macro repeatAt loop L1
  jmp L2 L1 jmp repeatAt L2
• endm

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Local Label (cont.)

• Now lets use it Loop1
  mNearLoop Loop1
• This expands to Loop1
  loop L1 jmp L2 L1 jmp Loop1 L2

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Local Label (cont.)

• Now lets use it again in the same programLoop2
  mNearLoop Loop2
• This expands to Loop2
  loop L1 jmp L2 L1 jmp Loop2
  L2

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Local Label (cont.)

• Solution
• mNearLoop macro repeatAt local L1, L2
  loop L1 jmp L2 L1 jmp
  repeatAt L2endm

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Local Label (cont.)

• Now lets use itLoop1
  mNearLoop Loop1
• This expands to Loop1
  loop ??0000 jmp ??0001 ??0000 jmp
  Loop1 ??0001

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General format

• macroname macro param1, param2, statement
  listendm
• Use "" for comments that are not copied every
  time the macro is used.
• Use REQ for required parameters
• Terminology We may "invoke", "expand", or
  "call" a macro