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lets say I want to move from one memory point to another lets say for now the text screen, (seg is 0b800h and it's size is 4000 bytes) so we have to use some very special command : MOVSB - Moves string byte, moves one byte from DS:SI to ES:DI and if the CF is 0 (CLD is the command thats set is to 0) then both si and di are incremented, if CF is 1 then (STD) si and di are decremented. MOVSW - Moves string word, moves one word (2 bytes) from DS:SI to ES:DI the method of incrementing is the same like movsb just it does it by 2 and by 1 byte. REP command - Repeats a certain command lets say "rep movsw" it will preform movsw in a loop and which cx defines how much, if cx is 10 then the movsw will be done 10 times. now after we know those command lets implement them !!!!!!!!!!!!!!!!! sseg segment db 10 dup (?) ends cseg segment assume cs:cseg,ss:sseg,ds:cseg,es:nothing buf db 4000 dup (?) start : push ds ; we must save it mov ax,seg buf ; we cannot type into segment registers directly mov ds,ax ; it goes into simple register and then to the segment mov si,offset buf mov ax,0b800h ; adress of screen mov es,ax mov di,0 mov cx,2000 ; to speed up use movsw (4000 bytes/2) rep movsw pop ds mov ax,4c00h int 21h ends end start end and thats is, but what I will do if I want lets say clear the memory with out using buffer or clearing the buffer it self ????
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LESSON6 - MEMORY MOVING |