Tell the Formula to scroll up the screen-00840
This subjective question is related to the book/course
vu cs507 Information Systems.
It can also be found in
vu cs507 Mid Term Solved Past Paper No. 2.
Question 1: Tell the Formula to scroll up the screen
scrollup: push bp
mov bp,sp
push ax
push cx
push si
push di
push es
push ds
mov ax, 80 ; load chars per row in ax
mul byte [bp+4] ; calculate source position
mov si, ax ; load source position in si
push si ; save position for later use
shl si, 1 ; convert to byte offset
mov cx, 2000 ; number of screen locations
sub cx, ax ; count of words to move
mov ax, 0xb800
mov es, ax ; point es to video base
Answer:
movsw scroll upscrollup: push bp
mov bp,sp
push ax
push cx
push si
push di
push es
push ds
mov ax, 80 ; load chars per row in ax
mul byte [bp+4] ; calculate source position
mov si, ax ; load source position in si
push si ; save position for later use
shl si, 1 ; convert to byte offset
mov cx, 2000 ; number of screen locations
sub cx, ax ; count of words to move
mov ax, 0xb800
mov es, ax ; point es to video base
