65d

; Example of how to write directly to screen memory, instead of
; using the *slow* BIOS function calls


        jmp start


scrmem dd 0B800:00000
str_1: db 'This is a test of writing directly to screen'
length equ $-str_1
col db 0
row db 0

start:
        call clrscr             ;Clear Screen

        mov cx,20               
        mov dx,0 by 10
  
again:
        push cx

        mov bl,1EH              ;Attribute
        mov si,str_1            ;Address of string
        mov cx,length           ;Length of string
        call write_str

        inc dh                  ;One row down
        pop cx
        loop again              ;Next string

        mov ah,00H              ;Wait for key
        int 16H


        call clrscr             ;Clear screen

        
        int 20H                 ;Exit to DOS




write_str:
        push dx
        push si
        push es
        les bp,scrmem
      
        sub ax,ax
        mov al,dh

        mov dh,160              ;Each row has 160 bytes...
        mul dh

        shl dl,1                
        add al,dl
        mov di,ax 
 
 
lp:
        movsb                      ;First the character...
        es mov b[bp+di],bl         ;then the attribute byte
        inc di
        loop lp

        pop es
        pop si
        pop dx
        ret


clrscr:
        push es
        les bp,scrmem
        mov di,0
        mov cx,2000
clr:    es mov b[bp+di],0
        inc di
        es mov b[bp+di],07H
        inc di
        loop clr        
        pop es
        ret
        
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