Capital

 1 assume cs:code, ds:data
 2 
 3 data segment
 4 
 5     db 'hello world'
 6     
 7 data ends
 8 
 9 code segment
10     
11     start: mov ax, data
12            mov ds, ax
13            mov bx, 0
14             
15            mov cx, 11
16            
17            call capital
18            mov ax, 4C00H
19            int 21H
20            
21     capital: and byte ptr [bx], 11011111B
22              inc bx
23              loop capital
24              ret
25 
26 code ends
27 
28 end start