1. CEN 226: Computer Organization & Assembly Language :CSC 225 (Lec#7)By
Dr. Syed Noman

2. Conditional statement: Program that checks even or odd for digits between 0 to 9
jmp exit print_odd: mov dx, offset msg3 exit: call puts mov ax,4c00h int 21h puts: mov ah, 9h int 21h ; output string ret getc: mov ah, 1h end
.model small .data msg1 db 13,10,’input a digit :: $’ msg2 db 13,10,’it is even :: $’ msg3 db 13,10, ’it is odd :: $’ .code mov mov ds,ax mov dx, offset msg1 call puts call getc mov dl,al and dl, b ; boolean stmt cmp dl,0 je print_even jmp print_odd print_even: mov dx, offset msg2

3. Implementing loop without loop statement
Printing ‘*’ ten times on the screen
mov ah,2
mov dl,’*’
mov cx,10
disp_char:
int 21h
dec cx
cmp cx,0
jne disp_char

4. General format for using loop instruction
mov cx, count ; count = # of times to repeat loop start_loop: ; use any label name <loop body> ; while cx > 0 ; repeat loop body instructions loop start_loop

5. Implementing loop with loop statement
mov ah,2
mov dl, ‘*’ ; al = ‘*’
mov cx, ; cx = 10 ; loop count
disp_char:
int 21h; display ‘*’
loop disp_char ; cx = cx - 1, if (cx != 0)
Here, cx is initialised to 10, the number of iterations required.
The instruction loop disp_char first decrements cx and then
tests if cx is not equal to 0, branching to disp_char only if cx
does not equal 0.

6. Loop Example with procedure
Example : Using loop instruction.
mov al, ‘*’ ; al = ‘*’
mov cx, ; cx = 10 ; loop count
disp_char:
call putc ; display ‘*’
loop disp_char ; cx = cx - 1, if (cx != 0)

7. Program to print name 10 times
.model small
.data
myName db 13,10,‘Dr. Syed Noman$’
.code
mov
mov ds,ax
mov cx,10
mov ah,9
mov dx, offset myName
again:
int 21h
loop again
mov ax,4c00h
end

8. Program to print name 10 times (with procedure)
.model small
.data
myName db 13,10,‘Dr. Syed Noman$’
.code
mov
mov ds,ax
mov cx,10
mov dx, offset myName
again:
call puts
loop again
mov ax,4c00h
int 21h
puts:
mov ah, 9h
int 21h ; output string
ret
end

9. Program print digits from 0 to 9
.model small
.code
mov cx,10
mov ah,2
mov dl,30h; mov dl, ‘0’; mov dl,48; mov dl, b
again:
int 21h
inc dl
loop again
mov ax,4c00h
end

10. Program print digits from 0 to 9 (with procedure)
.model small
.code
mov cx,10
mov dl,30h
again:
call putc
inc dl
loop again
mov ax,4c00h
int 21h
putc:
mov ah, 2h
ret
end

11. Program print digits from 0 to 9,with procedure
Program print digits from 0 to 9,with procedure. Use appropriate message)
.model small
.data
msg db 13,10, ‘Decimal Digits:’, 13,10, ‘$’
.code
mov
mov ds,ax
mov dx, offset msg
call puts
mov cx,10
mov dl,30h
again:
call putc
inc dl
loop again
mov ax,4c00h
int 21h
puts:
mov ah, 9h
int 21h ; output string
ret
putc:
mov ah, 2h
end

12. Program print even numbers from 0 to 9
.model small
.code
mov cx,5
mov ah,2
mov dl,30h
again:
int 21h
add dl,2
loop again
mov ax,4c00h
end

13. Program print even numbers from 0 to 9 (with procedure)
.model small
.code
mov cx,5
mov dl,30h
again:
call putc
add dl,2
loop again
mov ax,4c00h
int 21h
putc:
mov ah, 2h
ret
end

14. Nested loops
.data count dd ? .code mov cx,value ; set outer loop count L1: mov count, cx ; save outer loop count mov cx,New_value ; set inner loop count L2: ;(inner loop code) loop L2 ; repeat the inner loop mov cx,count ; restore outer loop count loop L1 ; repeat the outer loop

15. Practice Program in Class
Write an assembly code that prints the numbers from 1 to 4, 6 times on the screen. Each sequence of numbers from 1 to 4 are separated by new line.
Output:

16. DUP Operator
Use DUP to allocate (create space for) an array or string.
Syntax:
Counter DUP ( argument )
Counter and argument must be constants or constant expressions.

17. DUP Operator … .model small .data
msg db ‘Printing Alphabets count corresponding to position:’, 13,10
db “a”,13,10,
db “bb”,13,10
db “ccc”,13,10
db “dddd”,13,10,’$’
msg2 db ‘Printing Alphabets count corresponding to position:’, 13,10
db 1 dup (‘a’)
db 2 dup (‘b’)
db 3 dup (‘c’)
db 4 dup (‘d’)
.code
mov
mov ds,ax …

18. Assignment#2e, 2f, 2g
Write program with procedures, message to print numbers from 9 to 0.
Ask the count from the user to print his name. minimum zero, maximum 9. (Hint: put the value in cl, make ch zero)
Write program with procedure and message, to print odd numbers between 9 to 0 inclusive.

19. Assignment#2h
Print the following output on the command window using the DUP Operator:
********
******
**** **

20. Assignment#2i
Write an assembly code that prints the following on the console. 1
1 2
1 2 3