Author Topic: need help scrolling text mode screen DOWN  (Read 42 times)

Offline bilsch01

  • New Member
  • Posts: 1
need help scrolling text mode screen DOWN
« on: December 05, 2019, 05:53:42 AM »
My program uses 4000 bytes at segment 0xb800 for text mode display. The bottom 3 lines of the screen (160 bytes of memory per line) are static display and are not to be moved. Bytes 0 thru 3519 contain part of a text document and are the area to be moved up/down.

1. The code below moves the displayed document text up one line. It works fine:

mov ax,0xb800
mov ds,ax
mov es,ax
mov cx,1680
mov si,160
mov di,0
rep movsw

2. I tried the code below to move the displayed document text DOWN  one line:

mov ax,0xb800
mov ds,ax
mov es,ax
mov cx,1680
mov si,3200
mov di,3360
rep movsw

It moves the line beginning at b800:3200 down one line on the screen but the lines above it are not moved down. It is unfortunate that the static display gets overwritten, I can handle that later. I tried some variations of the code but I wasn't able to get the entire document area to move down one line. Can someone here tell me how to move the document area down one line.
TIA.   Bill S.

Offline fredericopissarra

  • Jr. Member
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  • Posts: 55
Re: need help scrolling text mode screen DOWN
« Reply #1 on: December 05, 2019, 11:34:45 AM »
The problem is overlapping data...

Try to point ES:DI to the end of the last line and DS:SI to the end of the line above, CX to 80*24, change the DF to 1 and do REP/MOVSW:

Code: [Select]
; OBS: destroys ax,cx, si and di.
scrolldown1line:
  push ds
  push es
  mov ax,0xb8000
  mov ds,ax
  mov es,ax
  mov di,160*25-2
  mov si,160*24-2
  mov cx,80*24
  std       ; to move backwards
  rep movsw
  cld
  pop es
  pop ds
  ret