Topics Introduction to Microprocessors. Chapter 5 Macros and modules. What is macro? How to use macro? (I) How to use macro?

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1 Topics Introduction to Microprocessors Macros Subroutines Modules Chapter 5 Macros and modules Suree Pumrin,, Ph.D Introduction to Microprocessors 2 What is macro? It is used to automate complex or repetitive tasks. Reduce the time to write the same task Reduce the possibility of errors Macro definition has three parts: (1) directive, (2) directive, and (3) body of the in between and Name dummy1, dummy2,, dummyn How to use macro? (I) Create a definition with a unique name. Invoke the for its service. Example of definition named Display display string1 AH, 09 DX, offset string Introduction to Microprocessors Introduction to Microprocessors 4 SEGMENT How to use macro? (II) DDD message1 DB name DB S ; Display message Display name ; My name$ is MIKE$ Code segment How to use macro? (III) The instruction Display message1 and Display name invokes the macro. The assembler expands Display message1 to the following codes in the.lst. file: 1 AH, 09 1 DX, offset message1 1 (1) indicates that the code is from the macro Introduction to Microprocessors Introduction to Microprocessors 6 1

2 Setting the cursor position cursor ; This macro sets the cursor location to row, column ;; Using BIOS 10H function 02 AH, 02 ; set cursor function BH, 00 ; page 00 DH, row ; row position DL, column ; column position 10H Clearing the screen clearscr ; This clears the screen ;; Using 10H function 06 AX, 0600H ;scroll screen function BH, 07 ; normal attribute CX, 0 ; from row 00, column 00 DX, 184FH ; to row 18H, column 4FH 10H Introduction to Microprocessors Introduction to Microprocessors 8 Local directive in macros All labels in the label field must be declared LOCAL. The LOCAL directive must be defined right after the directive. The LOCAL directive is used to declare all names and labels: LOCAL name1, name2, name3 or LOCAL name1 LOCAL name2 LOCAL name3 Word multiplication (I) MULTIPLY value1, value2, result LOCAL BACK ; This macro computes result = value1 x value2 ;; By repeated addition ;; value1 and value2 are word operands; ;result is doubleword BX, value1 ; BX is a multiplier CX, value2 ; CX is a multiplicand SUB AX, AX ;clear AX DX, AX ;clear DX BACK: ADD AX, BX ; Add BX to AX ADC DX, 00 ; Add carries if there is one Loop BACK ; continue until CX = 0 result, AX ; save the low word result+2, DX ; save the high word Introduction to Microprocessors Introduction to Microprocessors 10 Word multiplication program using definition MULTIPLY VALUE1, VALUE2, RESULT LOCAL BACK ;THIS COMPUTES RESULT = VALUE1 X VALUE2 ;;BY REPEATED ADDITION RESULT1 ;;VALUE1 AND VALUE2 ARE WORD OPERANDS; RESULT2 RESULT IS A DOUBLEWORD RESULT3 BX,VALUE1 ;BX=MULTIPLIER CX,VALUE2 ;CX=MULTIPLICAND SUB AX,AX ;CLEAR AX DX,AX ;CLEAR DX BACK: ADD AX,BX ;ADD BX TO AX ADC DX,00 ;ADD CARRIES IF MULTIPLY 2000,500,RESULT1 THERE IS ONE MULTIPLY 2500,500,RESULT2 LOOP BACK ;CONTINUE UNTIL CX=0 MULTIPLY 300,400,RESULT3 RESULT,AX ;SAVE THE LOW WORD RESULT+2,DX;SAVE THE HIGH WORD ;GO BACK TO DOS Include directive (I) Saved these definitions as MY2.MAC cursor ; This macro sets the cursor location to ;; Using BIOS 10H function 02 AH, 02 ; set cursor function BH, 00 ; page 00 DH, row ; row position DL, column; column position 10H display string1 AH, 09 DX, offset string1 clearscr ; This clears the screen ;; Using 10H function 06 AX, 0600H ;scroll screen function BH, 07 ; normal attribute CX, 0 ; from row 00, column 00 DX, 184FH; to row 18H, column 4FH 10H Introduction to Microprocessors Introduction to Microprocessors 12 2

3 Include directive (II) TITLE PROG5-3 INCLUDE MY2.MAC MESSAGE1 DB 'This is a test of macro concepts','$' CLEARSCR ;INVOKE CLEAR SCREEN DISPLAY MESSAGE1 ;INVOKE DISPLAY ;GO BACK TO DOS Subroutines It is also known as a procedure. A single instruction call is used in the body to call the subroutine. The contents of the next instruction IP or CS and IP in the body are saved on the stack. A return instruction is included at the end of the subroutine to initiate the return sequence to the program Introduction to Microprocessors Introduction to Microprocessors 14 Subroutine call instruction Return instruction Mnemonic CALL Meaning Subroutine call Format CALL operand Operation Execution continues from the address of the subroutine specified by the operand. IP and CS of the next instruction upon return are saved on the stack Flags Affected Mnemonic Meaning Return Format (F) or (F) operand Operation Return to the program by restoring IP (and CS for far-proc). If there is operand, it is added to the contents of SP. Flags Affected Allowed operands Operand Near-proc Far-proc Memptr16 Regptr16 Memptr Introduction to Microprocessors 15 Allowed operands Operand Disp Introduction to Microprocessors 16 Near Call Far Call CALL proc1; push IP (return address) proc1 near ; pop IP Proc1 CALL proc2; push CS push IP (CS:IP = return address) proc2 F; pop IP pop CS proc Introduction to Microprocessors Introduction to Microprocessors 18 3

4 Modules Efficient way to develop software: Treat each subroutine as a separate program (or module) with a separate filename. Test each program then link them together. Linking modules EXTRN directive PUBLIC directive directive in modules EXTRN directive A directive for names and variables that are defined outside the present module EXTRN format EXTRN name1:type EXTRN name2:type EXTRN name1:type, name2:type External directive when it refers to a procedure NEAR,, or Example: EXTRN sum:far EXTRN clear:near External directive when it refers to a data item BYTE, WORD, DWORD, FWORD, QWORD, or TBYTE Example: EXTRN data1:byte EXTRN ten:word Introduction to Microprocessors Introduction to Microprocessors 20 PUBLIC directive A directive for names and parameters in the present module that are defined as EXTRN elsewhere The assembler and linker can match the defining names and parameters for the corresponding EXTRN and PUBLIC ones. PUBLIC directive format PUBLIC name1 PUBLIC name2 PUBLIC name1, name2 Example: PUBLIC message1 directives The module calls modules (subroutines) with no label or name after the directive. Example modules: 1.asm, proc1.asm, and proc2.asm Compile source file to generate.obj. file 1.asm proc1.asm proc2.asm Linking modules under the filenames: 1.obj, proc1.obj, and proc2.obj C> tlink 1 proc1 proc Introduction to Microprocessors Introduction to Microprocessors 22 A shell for modular programming.stack 64.data ; EXTRN subprog1: EXTRN subprog2: mov ax,@data mov ds,ax call subprog1 call subprog2 mov ah, 4ch 21h ;----- in a separate file;-- PUBLIC subprog1 subprog1 subprog1 ;----- in a separate file;-- PUBLIC subprog2 subprog2 subprog2 ; Introduction to Microprocessors 23 ASCII to Binary conversion module TITLE PROG7-6 6 ASCII TO BINARY CONVERSION MODULE ;this module converts any ASCII number between 0 to to binary ;CALLING PROGRAM SETS ; SI = OFFSET OF ASCII STRING ; BX = STRING LENGTH - 1 (USED AS INDEX O ASCII NUMBER) ;THIS MODULE SETS ; AX = BINARY NUMBER ; EXTRN TEN:WORD PUBLIC ASC2B_CON ASC2B_CON PUSHF ;STORE REGS CHANGED IN THIS MODULE PUSH DI PUSH CX SUB DI,DI ;CLEAR DI FOR THE BINARY(HEX) RESULT CX,1 ;CX = WEIGHT FACTOR A2B_LOOP: AL,[SI+BX] ;GET THE ASCII DIGIT AND AL,0FH ;STRIP OFF '3' SUB AH,AH ;CLEAR AH FOR WORD MULTIPLICATION MUL CX ;MULTIPLY BY THE WEIGHT ADD DI,AX ;ADD IT TO BINARY (HEX) RESULT AX,CX ;MULTIPLY THE WEIGHT FACTOR MUL TEN ; BY TEN CX,AX ; FOR NEXT ITERATION DEC BX ;DECREMENT DIGIT POER JNS A2B_LOOP ;JUMP IF OFFSET >=0 AX,DI ;STORE BINARY NUMBER IN AX POP CX ;RESTORE FLAGS POP DI POPF ASC2B_CON Introduction to Microprocessors 24 4

5 Passing parameters among modules Parameters can be passed from one module to another through registers, memory, or the stack. Passing parameters via registers It is widely used in many DOS and BIOS interrupt function calls. The next example-- --calling module-- demonstrated this method Introduction to Microprocessors 25 Calling module TITLE PROG7-7 7 CALLING PROGRAM TO EXTRN ASC2B_CON: CONVERT ASCII TO BINARY ; PUBLIC TEN ;DISPLAY THE PROMPT AH,09 DX,OFFSET PROMPT1 - ;INPUT STRING ASC_AREA LABEL BYTE AH,0AH MAX_LEN DB 6 DX,OFFSET ASC_AREA ACT_LEN DB? ASC_NUM DB 6 DUP (?) SI,OFFSET ASC_NUM ORG 10H BH,00 BINNUM DW 0 BL,ACT_LEN PROMPT1 DB 'PLEASE ENTER A 5 DIGIT DEC BX NUMBER','$' CALL ASC2B_CON TEN DW 10 BINNUM,AX ;SAVE THE BINARY - (HEX) RESULT ;GO BACK TO DOS Introduction to Microprocessors Passing parameters via memory and stack Passing parameters via memory Defining a memory area and passing parameters to these memory location Passing parameters via the stack Parameters are stored on the stack by the routine and retrieved from the stack by the called subroutine. Passing parameters via the stack ( program) TITLE PROG7-8 8 PASSING PARAMETERS VIA THE STACK ; EXTRN SUBPROG6: ; ; VALUE1 DW 3F62H VALUE2 DW 1979H VALUE3 DW 25F1H RESULT DW 2 DUP (?) ; PUSH VALUE3 ;SAVE VALUE3 ON STACK PUSH VALUE2 ;SAVE VALUE2 ON STACK PUSH VALUE1 ;SAVE VALUE1 ON STACK CALL SUBPROG6 ;CALL THE ADD ROUTINE RESULT,AX ;STORE RESULT+2,BX ; THE RESULT Introduction to Microprocessors Introduction to Microprocessors 28 Passing parameters via the stack (module file) ;--- in a separate file: TITLE SUBPROG6 MODULE TO ADD THREE WORDS BROUGHT IN FROM THE STACK PUBLIC SUBPROG6 SUBPROG6 SUB BX,BX ;CLEAR BX FOR CARRIES PUSH BP ;SAVE BP BP,SP ;SET BP FOR INDEXING AX,[BP]+6 ; VALUE1 TO AX CX,[BP]+8 ; VALUE2 TO CX DX,[BP]+10 ; VALUE3 TO DX ADD AX,CX ;ADD VALUE2 TO VALUE1 ADC BX,00 ;KEEP THE CARRY IN BX ADD AX,DX ;ADD VALUE3 ADC BX,00 ;KEEP THE CARRY IN BX POP BP ;RESTORE BP BEFORE URNING 6 ;URN AND ADD 6 TO SP TO BYPASS S DATA SUBPROG Introduction to Microprocessors 29 5