string instruction with repeated(REP)

1- move from block to another by using string instruction with repeated(REP) :

org 100h

mov ax,0h

mov ds,ax

mov es,ax

mov si,2000h  

mov di,3000h

mov cx,20h    // 32 consecutive bytes in hex=20

cld

rep movsb

hlt

2-scan number if find replace with another number else by default found in last location :

org 100h  

cld 

mov ax,0h

mov es,ax

mov ds,ax  

mov di,00d0h  

mov [di],45h // for certain replace else put 29 in the last location 

mov cx,0046h // 70 bytes

mov al,45h

repne scasb

dec di

mov byte ptr[di],29h

hlt