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More about procedures and Video Processing

More about procedures and Video Processing. Lesson plan. Review existing concepts More about procedures and boolean expression Video processing. Review. Procedure: name PROC ; the code of the procedure ... RET name ENDP Calling a procedure: CALL <name of the procedure>

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More about procedures and Video Processing

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  1. More about proceduresand Video Processing

  2. Lesson plan • Review existing concepts • More about procedures and boolean expression • Video processing

  3. Review • Procedure: name PROC ; the code of the procedure ...RETname ENDP • Calling a procedure: CALL <name of the procedure> Address of the next instruction will be pushed onto STACK

  4. More about procedures • Passing parameters: • Are very similar to the concept of passing parameters in C/C++ and Java • A program may pass parameters by: • Value • Reference

  5. Passing parameters by value: • Parameters are the actual data item. Passing value in register: • Store values being passed in registers • Call the procedure Example: MOV AX, operand1 MOV BX, operand2 CALL MULTIPROC … MULTIPROC PROC MUL BX RET MULTIPROC ENDP MULTIPROC(operand1,operand2

  6. Passing parameters by value: Passing value in STACK • Push values being passed in STACK • Call the procedure • Pop values from STACK Example: PUSH operand1 PUSH operand2 CALL MULTIPROC … MULTIPROC PROC PUSH BP MOV BP, SP MOV AX, [BP+8] MUL WORD PTR [BP+4] POP BP RET MULTIPROC ENDP MULTIPROC(operand1,operand)

  7. Passing parameters by value: Passing value in STACK: Address the limitations in terms of number of registers More complicated because we need indirect addressing to access the stack (use of BP)

  8. Passing parameters by value: Operand1 DW 10 ; (0AH) Operand2 DW 2 ; (02H) PUSH BP ;to save its content

  9. Passing parameters by Reference • Instead of passing values, we pass the address using register or stack • LEA SI, operand1 • LEA DI, operand2 • CALL MULTIPROC • MULTIPROC PROC • MOV AX, [SI] • MUL [DI] • RET • MULTIPROC ENDP MULTIPROC(&operand1, &operand2)

  10. Passing parameters by Reference • Instead of passing values, we pass the address using register or stack • PUSH OFFSET operand1 • PUSH OFFSET operand2 • CALL MULTIPROC • …… • MULTIPROC PROC • PUSH BP • MOV BP, SP • MOV BX, [BP+6] • MOV DI,[BP+4] • MOV AX, [BX] • MUL WORD PTR [DI] • POP BP • RET 4 • MULTIPROC ENDP MULTIPROC(&operand1, &operand2)

  11. Video processing • Use INT instruction to handle inputs and outputs • INT 10H: screen handling • INT 21H: for displaying screen output • Main idea: • Insert a value in AH register which is used to identify the type of service the interrupt needs to perform

  12. Screen features • 25 rows (0-24) and 80 columns (0-79) (0,79) (0,0) (24,0) (24,79)

  13. Screen features • Cursor location: Upper left corner: Row: 0, Column 0 Upper right corner: Row: 0, Column 79 Lower left corner: Row: 24, Column 0 Lower right corner: Row: 24, Column 79 Center: Row 12, Column 39

  14. Screen features Video Display Area: Text mode: 4KB in BIOS (2K for characters and 2K for attributes) Pages: 0 to 7 INT 10H: Set cursor (AH= 02H) INT 10H: Clear & Scroll screen (AH = 06H)

  15. Screen features Setting cursor: INT 10H function 02H tells BIOS to set the cursor • Step 1: Determine the row and column that we want to set our cursor at. E.g row = 12, column = 40) • Step 2: Load 02H to AH. Load page# to BH, Row# to DH, and Column# to DL • Step 3: Call INT 10H function

  16. Screen features Example: Set cursor at (12,40) MOV AH, 02H MOV BH, 0 ; page# to BH MOV DH, 12 ; row# to DH MOV DL, 40 ; column# to DL INT 10H

  17. Screen features • Clear & Scrolling screen INT 10H function 06H tells BIOS to clear or scroll screen • Step 1: Load 06H to AH • Step 2:Determine number of lines to scroll • Step 3:Determine the attributes of the screen (background and foreground colors). Load them into BH • Step 4: Load the starting row:column to CX • Step 5: Load the ending row:column to DX • Step 6: Call INT 10H

  18. Screen features • Example: MOV AH,06H ;clear and scroll MOV AL,00H MOV BH,0F1H ;white background, blue foreground MOV CX,0000H ;starting row:column MOV DX,184FH ;ending row:column INT 10H

  19. Screen features • Attribute byte in text mode determines the characteristics of each displayed character 71=0111 0001 (White background and Blue foreground)

  20. Screen features • INT 21H: Display ASCII characters (02H) Display string (09H or 40H) Get input from keyboard (0AH or 3FH)

  21. Screen features • Display a character • Step 1: Set AH =02H • Step 2: Load the character to DL • Step 3: Call INT 21H to display the character

  22. Screen features Example: MOV AH, 02H MOV DL, ‘C’ INT 21H

  23. Practice/Lab 1 • Open your browser and open this page: C:\emu8086\documentation\8086_instruction_set.html And C:\emu8086\documentation\8086_and_dos_interrupts.html 2. Open your emu8086 software 3. Cut and paste (or type) the following code (as shown in the next page) and save as output.asm

  24. Practice/Lab 1 page 60,132 TITLE VideoPractice ClearScreen and Output ; --------------------------------------------- STACK SEGMENT PARA STACK 'Stack' DW 32 DUP(0) STACK ENDS ; ---------------------------------------------- DATASEG SEGMENT PARA 'Data' ; Please insert your data declaration here DATASEG ENDS CODESEG SEGMENT PARA 'Code' MAIN PROC FAR MOV AX, dataseg MOV DS, AX ; Please enter your code here MOV AX,4C00H ;exit procedure INT 21H MAIN ENDP CODESEG ENDS END MAIN ;End of program

  25. Practice/Lab 1 4.Modify your code so that it performs the following tasks: Clear screen Set cursor to the middle of screen Display the characters (5) in: CHAR_TBL DB ‘A’ ,’B’, ’C’, ’D’, ’E’ on the middle of the screen 5. Compile and run your code

  26. Answer to Fibonaci practice FIBONACI PROC NEAR MOV AX,00 MOV BX,01 MOV CX,7 ;7 repetitions MOV DX,00 L10: ADD AX,BX ;Number is in AX MOV BX,DX MOV DX,AX LOOP L10 RET FIBONACI ENDP

  27. INT 21H displaying screen • INT 21H, function 09H: display a string which is followed by the dollar($) sign • Step 1: Declare a string, which is followed by dollar sign • Step 2: Set DS to the beginning address of data segment. And set AH =09H • Step 3: Load offset of the string to DX • Step 4: Call INT 21H

  28. INT 21H displaying screen • Example: message db "Hello everybody! I am learning assembly language!","$“ mov ah,09 ; move 9 to AH lea dx,message int 21h

  29. INT 21H displaying screen • INT 21H, function 40H • Use file handles to process display operations • Procedure: • Step 1: Set AH=40H • Step 2: Set BX= file handle (of screen) • Step 3: Set CX = number of characters to display • Step 4: Set DX = Offset Address of display area • Step 5: Call INT 21H

  30. INT 21H displaying screen • File handle: is a number used to refer to a specific device Handle Device 00 Input (keyboard) 01 Output (screen) 04 Printer

  31. INT 21H displaying screen • Example: message db ‘Hello’, 0DH, 0AH MOV AH,40H ; move 40H to AH MOV BX, 01 MOV CX, 7 lea dx,message int 21h

  32. INT 21H for keyboards • INT 21H function: • 0AH: input from keyboard • 3FH: input from keyboard

  33. INT 21H for keyboards • INT 21H function 0AH • Step 1:Set AH = 0AH • Step 2: Load offset address of the parameter list into DX • Step 3: Call INT 21H

  34. INT 21H for keyboards • Parameter list is a structure which consists of: <Name of parameter list> LABEL BYTE <Variable represents maximum number of input characters> DB <value> <Variable represents actual number of input characters> DB <value> <Variable to contain typed characters>

  35. INT 21H for keyboards • Example: Para_list label byte max_len DB 100 act_len DB ? input DB 100 DUP(‘ ‘) MOV AH, 0AH LEA DX, Para_list INT 21H

  36. INT 21H for keyboards • Example: • Assume the input string is ‘CS271’ act_len = 5 input: CS271$ ‘ ‘ ‘ ‘ ‘ ‘ ‘ ‘ MOV BH, 00 MOV BL, ACT_LEN MOV INPUT[BX],’$’ CS271$

  37. INT 21H function 3F • This uses file handles to request keyboard input • Step 1: Set AH = 3FH • Step 2: Set BX=00H (file handle 00 represents keyboard) • Step 3: Set CX = maximum number of character to accept • Step 4: Load offset address of area for entering characters to DX

  38. INT 21H function 3F • Example: input DB 100 DUP(‘ ‘) MOV AH, 3FH MOV BX, 00H MOV CX, 100 LEA DX, input INT 21H

  39. INT 21H function 3F • Example: (not available in EMU8086) input DB 100 DUP(‘ ‘) MOV AH, 3FH MOV BX, 00H MOV CX, 100 LEA DX, input INT 21H

  40. Practice/Lab 2 • Open your browser and open this page: C:\emu8086\documentation\8086_instruction_set.html And C:\emu8086\documentation\8086_and_dos_interrupts.html 2. Open your emu8086 software 3. Cut and paste (or type) the following code (as shown in the next page) and save as input.asm

  41. Practice/Lab page 60,132 TITLE InputPRactice Input ; --------------------------------------------- STACK SEGMENT PARA STACK 'Stack' DW 32 DUP(0) STACK ENDS ; ---------------------------------------------- DATASEG SEGMENT PARA 'Data' ; Please insert your data declaration here DATASEG ENDS CODESEG SEGMENT PARA 'Code' MAIN PROC FAR MOV AX, dataseg MOV DS, AX ; Please enter your code here MOV AX,4C00H ;exit procedure INT 21H MAIN ENDP CODESEG ENDS END MAIN ;End of program

  42. Practice/Lab 4.Modify your code so that it performs the following tasks: - Read a string (length <= 50) from keyboard. You need to insert the following into your data declaration Para_list label byte max_len DB <put the maxlen for this exercise> act_len DB ? input DB <replace with the maxlen for this exercise> DUP(‘ ‘) - Display the string on the screen at (12,40) 5. Compile and run your code

  43. Project 2

  44. Adavanced Screen Processing • Explore INT 10H to: • Set video mode • Display attribute or character at cursor position

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