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                Blinking Lights on Keyboard 
                 
                -------------------------------------------------------------------------------- 
                 
                Description : This is a TSR program. It hooks itself with the 
                timer interrupt and automaticcy lights on/off the Num, Caps and 
                Scroll Lock keys LEDs on the keyboard. It is a fun to watch.  
                 
                #include<dos.h> 
                void interrupt mytimer(); 
                void interrupt (*prev)(); 
                int run=0,lt=0,ticks=0; 
                char far *mode; 
                int temp; 
                void main() 
                { 
                mode=(char far*)0x417; 
                prev=getvect(0x8); 
                setvect(0x8,mytimer); 
                keep(0,100); 
                getch(); 
                } 
                void interrupt mytimer() 
                { 
                if(run==0) 
                { 
                ticks++; 
                if(ticks==5) 
                { 
                ticks=0; 
                run=1; 
                lt++; 
                if(lt==1) 
                { 
                temp=*mode; 
                temp=temp&0x8f; 
                temp=temp|0x40; 
                *mode=temp; 
                } 
                else if(lt==2) 
                { 
                temp=*mode; 
                temp=temp&0x8f; 
                temp=temp|0x20; 
                *mode=temp; 
                } 
                else if(lt==3) 
                { 
                temp=*mode; 
                temp=temp&0x8f; 
                temp=temp|0x10; 
                *mode=temp; 
                lt=0; 
                } 
                } 
                run=0; 
                } 
                (*prev)(); 
                } 
                 
                 
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