seg_a		segment	byte public
		assume	cs:seg_a, ds:seg_a

		org	100h
               
timer           proc    far
start:
                mov al,36h  ; channel 0 and modes
                out 43h,al  ; command register
                mov ax,450h ; counter 
                out 40h,al  ; counter to channel 0
                mov al,ah
                out 40h,al
                int 20h
timer           endp
seg_a		ends
		end	start