screen = 2000                   ;the number of blocks on the screen
delay = 100                     ;the amount of delay, used in Wait1

.model small
.stack 100h
.data
.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:       mov al,11h          ;will cause ColorScreen to fill the screen with ASCII
            call ColorScreen 
            call Wait1          ;wait 100
            mov al,20h          ;will cause ColorScreen to fill the screen with attribute 20h
            call ColorScreen
            call Wait1          ;wait 100
            mov al,0            ;will cause ColorScreen to clear out the screen of value and attribute
            call ColorScreen    
            call Wait1          ;wait 100
            mov al,11h          ;will cause ColorScreen to fill the screen with ASCII
            call ColorScreen
            
finish:     mov ah,4ch          ;program termination - return control to OS
            int 21h
;**********************
Wait1:      mov cx,delay        ;this function waits for the amount of time delay has been set to                            
waitAgain:  loop waitAgain
    ret
         
ColorScreen:cmp al,0            ;checks value of al to activate specific commands
            je zeroScreen       ;al = 0: calls zeroScreen
            cmp al,11h          
            je fullScreen       ;al = 11h: calls fullScreen

normalScreen:                   ;colors the entire screen with the given al attribute
            mov bx,1
            mov cx,screen
NSLoop:     mov es:[bx],al
            add bx,2
            loop NSLoop
    ret
            
fullScreen: mov bx,0            ;fills the entire screen with ASCII
            mov cx,screen
            mov ah,0    
FSLoop:     mov es:[bx],ah
            add ah,1
            add bx,2
            loop FSLoop
    ret
    
zeroScreen: mov bx,0            ;clears the entire screen of value and attribute
            mov cx,screen
ZSLoop:     mov es:[bx],al
            mov es:[bx+1],7
            add bx,2
            loop ZSLoop
    ret           
            
end