line = 160                      ;the number of blocks on a line

.model small
.stack 100h
.data 

place dw 0                      ;keeps the current location of dropped letter (range: 0-79)
delay db ?                      ;the amount of delay, used in Wait1

.code
;*********************MAIN
initialize: mov ax,@data        ;program initialization: set @data, set mode text screen
            mov ds,ax
            mov ax,0b800h
            mov es,ax
            mov ax,3
            int 10h

main:       call ColorScreen    ;fills 2 lines of junk ASCII
            mov ax,2            ;fixes an error caused with odd numbers
            mul place
            mov place,ax
            mov bx,place        ;the place from which to start dropping
            mov al,80          
chain:      call DropLetter     ;drops letters 80 times
            sub al,1
            jnz chain
            
            
finish:     mov ah,4ch          ;program termination - return control to OS
            int 21h
;**********************
Wait1:      mov ch,delay        ;this function waits for the amount of time delay has been set to                            
waitAgain:  sub ch,1
            jnz waitAgain
    ret       
    
DropLetter: mov cx,12           ;step 0
            mov dx,es:[bx]
            mov ah,es:[bx+160]
            mov si,es:[bx+320]
            mov es:[bx],0
top:        add bx,160          ;step 1  
            mov es:[bx],dx
            mov es:[bx],ah      ;step 2
            mov es:[bx+160],dx
            mov ah,es:[bx+320]
            mov es:[bx+160],si  ;step 3
            mov es:[bx+320],dx
            mov si,es:[bx+480]
            add bx,160
            loop top
            
            add place,2         ;done dropping letter, move to next letter to drop
            mov bx,place
    ret        

ColorScreen:mov bx,0            ;fills ASCII for as many lines as requested
            mov cx,line
            mov ah,0    
FSLoop:     mov es:[bx],ah
            add ah,1
            add bx,2
            loop FSLoop
    ret      
            
end