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 Address of the next instruction will be pushed onto STACK

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

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 … MULTIPROCPROC MUL BX RET MULTIPROCENDP MULTIPROC(operand1,operand2

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 … MULTIPROCPROC PUSH BP MOV BP, SP MOV AX, [BP+8] MUL WORD PTR [BP+4] POP BP RET MULTIPROCENDP MULTIPROC(operand1,operand)

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)

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

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

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

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

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

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

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)

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

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

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

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

Screen features –Attribute byte in text mode determines the characteristics of each displayed character 71= (White background and Blue foreground)

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

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

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

Practice/Lab 1 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

Practice/Lab 1 page 60,132 TITLEVideoPracticeClearScreen and Output ; STACKSEGMENT PARA STACK 'Stack' DW 32 DUP(0) STACKENDS ; DATASEGSEGMENT PARA 'Data' ; Please insert your data declaration here DATASEGENDS CODESEG SEGMENT PARA 'Code' MAINPROC 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

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

Answer to Fibonaci practice FIBONACI PROC NEAR MOVAX,00 MOVBX,01 MOVCX,7;7 repetitions MOVDX,00 L10: ADDAX,BX;Number is in AX MOVBX,DX MOVDX,AX LOOPL10 RET FIBONACI ENDP

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

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

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

INT 21H displaying screen –File handle: is a number used to refer to a specific device HandleDevice 00Input (keyboard) 01 Output (screen) 04Printer

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

INT 21H for keyboards INT 21H function: –0AH: input from keyboard –3FH: input from keyboard

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

INT 21H for keyboards Parameter list is a structure which consists of: LABEL BYTE DB

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

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],’$’ CS271$

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 INT 21H function 3F

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

Practice/Lab 2 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 input.asm

Practice/Lab page 60,132 TITLEInputPRactice Input ; STACKSEGMENT PARA STACK 'Stack' DW 32 DUP(0) STACKENDS ; DATASEGSEGMENT PARA 'Data' ; Please insert your data declaration here DATASEGENDS CODESEG SEGMENT PARA 'Code' MAINPROC 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

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 act_lenDB ? input DB DUP(‘ ‘) - Display the string on the screen at (12,40) 5. Compile and run your code

Project 2

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