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Lesson plan
• Review existing concepts
• More about procedures and boolean expression
• Video processing
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
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, operand1MOV BX, operand2
CALL MULTIPROC…MULTIPROC PROC
MUL BXRET
MULTIPROC ENDP
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 operand1PUSH operand2
CALL MULTIPROC…MULTIPROC PROC
PUSH BPMOV BP, SPMOV AX, [BP+8]MUL WORD PTR [BP+4]POP BPRET
MULTIPROC ENDP
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, operand1LEA DI, operand2CALL MULTIPROC
MULTIPROC PROC MOV AX, [SI]MUL [DI]RET
MULTIPROC ENDP
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
……MULTIPROC PROC
PUSH BPMOV BP, SPMOV BX,
[BP+6]MOV DI,
[BP+4]MOV AX,
[BX]
MUL WORD PTR [DI]
POP BPRET 4
MULTIPROC ENDP
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
• 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=0111 0001 (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
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 1page 60,132TITLE 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 21HMAIN ENDP
CODESEG ENDSEND 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 MOV AX,00
MOV BX,01MOV CX,7 ;7 repetitionsMOV DX,00
L10:ADD AX,BX ;Number is in AXMOV BX,DXMOV DX,AXLOOP L10
RETFIBONACI 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
Handle Device
00 Input (keyboard)
01 Output (screen)
04 Printer
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
– 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:
<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>
INT 21H for keyboards
• Example:Para_list label byte
max_len DB 100act_len DB ?input DB 100 DUP(‘ ‘)
MOV AH, 0AHLEA DX, Para_listINT 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/Labpage 60,132TITLE 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 21HMAIN ENDP
CODESEG ENDSEND 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 declarationPara_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
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