Video processing The INT instruction enables program to interrupt its own processing. Use INT instruction to handle inputs and outputs

Transcription

1 Video processing The INT instruction enables program to interrupt its own processing. Use INT instruction to handle inputs and outputs INT 10H: screen handling INT 21H: for displaying screen output and accepting keyboard input INT 33H; Initialize mouse driver Main idea: Insert a value in AH register which is used to identify the type of service the interrupt needs to perform

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

3 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

4 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)

5 Screen features Setting cursor: INT 10H function 02H tells BIOS to set the cursor Idea Load 02H to AH. Load page# to BH, Row# to DH, and Column# to DL Call INT 10H function

6 Screen features Example: Set cursor at (12,40) MOV AH, 02H MOV BH, 0 MOV DH, 12 MOV DL, 40 INT 10H ; page# to BH ; row# to DH ; column# to DL mov DX,1240H

7 Clear & Scrolling screen Screen features 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

8 Screen features Example: MOV AH,06H MOV AL,00H MOV BH,71H ; clear and scroll ; full screen ;white background(7), blue foreground(1) MOV CX,0000H ;starting row:column MOV DX,184FH ;ending row:column INT 10H

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

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

11 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

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

13 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.h tml 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

14 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 INT 21H MAIN ENDP ;exit procedure CODESEG ENDS END MAIN ;End of program

15 Practice/Lab 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

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18 INT 21H displaying screen INT 21H, function 09H: display a string which is followed (terminated) 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

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

20 INT 21H for keyboards INT 21H function: 0AH: input from keyboard (print to file) Check from C:\emu8086\documentation\8086_and_dos_interrupts.html 3FH: input from keyboard (read from file) Check from C:\emu8086\documentation\8086_and_dos_interrupts.html 01H: input from keyboard

21 INT 21h/ 01H and 02H Input a character Step 1: Set AH =01H Step 2: : Call INT 21H to display the character Step 3: The input character is saved in AL To display the entered character Step 1: Set AH=02H Step 2: Load the character from AL to DL Step 3 Call INT 21H to display the character

22 Int 21h/1h 2h

23 Example Prompt reading a character

24 Enter/display character

25 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