.model      tiny

                .code
                org             0100h
main:
                ;   set display mode to text mode
                mov     ah, 0h
                mov     al, 3h
                int     10h

                mov     ah, 6h
                mov     al, 0h
                mov     bh, 70h
                mov     cx, 0000h
                mov     dx, 184fh
                int     10h

                ; set initial value for cursor position
                mov     dh, 0h  ;   row variable
                mov     dl, 0h  ; column variable
                mov     bh, 0h

printA: ; move cursor to desired position and print 'a'

                ; move cursor
                mov     ah, 2h
                int     10h

                ;   push current cursor position to stack
                push    dx

                ; wait with 10000 microsecs
                mov     ah, 86h
                mov     cx, 0000h
                mov     dx, 2710h
                int     15h

                ;   pop current cursor position from stack
                pop     dx

                ; print 'a'
                mov     ah, 9h  ; set to write character mode
                mov   cx, 1     ; print 1 character
                mov     bl, 70h ; set attribute for character
                mov     al, 61h ; set desired character to 'a'
                int     10h
                jmp     shiftPos

shiftPos:   ; decide if now on odd-indexed row or even-indexed row
                test    dh, 1h
                jz      evenShift   ; if on even-indexed, jump to evenShift

oddShift:   ; shift cursor index when in odd-indexed row
                dec     dl  ; decrease cursor column index (move cursor to the left)
                cmp     dl, 0   ; check if cursor is still in screen
                js      newlineEven ; if cursor is not in screen, go to newline
                jmp     printA  ; else continue printing 'a'

evenShift: ; shift cursor index when in even-indexed row
                inc     dl  ; increase cursor column index (move cursor to the right)
                cmp     dl, 50h ; check if cursor is still in screen
                jge     newlineOdd ; if cursor is not in screen, go to newline
                jmp     printA ; else continue printing 'a'

newlineEven: ; go to new line with even-indexed
                inc     dl ; increase cursor column index (move cursor back to screen)
                inc     dh  ; increase row index
                jmp     printA ; go to print 'a'

newlineOdd: ; go to new line with odd-indexed
                cmp     dh, 18h ; check if row index exceed 24
                jge     exit    ; if true, terminate program
                dec     dl  ; decrease cursor column index (move cursor back to screen)
                inc     dh  ; increase row index
                jmp     printA ; go to print 'a'

exit:
                ;   clear screen
                mov     ah, 6h
                mov     al, 0h  ; clear whole screen
                mov     bh, 7h
                mov     cx, 0h
                mov     dx, 184fh
                int     10h

                ret
                end     main