Another Example:

1. Another Example: #include<BIOS.H> #include<DOS.H> char st[80] ={"Hello World$"}; char st1[80] ={"Hello Students!$"}; void interrupt (*oldint65)( ); void interrupt newint65( ); void main() { oldint65 = getvect(0x65); setvect(0x65, newint65); keep(0, 1000); }

2. Continued: void interrupt newint65( ) { if (( _AH ) = = 0) { _AH = 0x09; _DX = (unsigned int) st; geninterrupt (0x21); } else { if (( _AH ) = = 1) { _AH = 0x09; _DX = (unsigned int) st1; geninterrupt (0x21); } } }

3. 2nd Program: #include<BIOS.H> #include<DOS.H> void main() { _AH = 1; geninterrupt (0x65); _AH = 0; geninterrupt (0x65); }

4. Interrupt Interception Hooks/Stealing

5. Execution Interrupted ISR Perform I/O Normal Execution of Interrupt

6. New Routine Original Routine Interrupt Interception

7. Original Routine New Routine Other form of Interrupt Interception

8. void Interrupt newint(); void Interrupt (*old)(); void main() { old=getvect(0x08); Setvect(0x08,newint); Keep(0,1000); } void interrupt newint () { (*old)(); }

9. Timer Interrupt

10. Hardware Interrupts • Invoked by Means of Hardware • Approximately occurs 18.2 times per second

11. BIOS Data Area 0040:0000

12. Insert key Right Shift key Caps Lock Key Left Shift Key Num Lock key Ctrl Key Scroll lock key Alt Key 40:17H Keyboard Status Word

13. #include <dos.h> void Interrupt (*old)(); void Interrupt new(); Char far *scr=(char far* ) 0x00400017; Void main() { old=getvect(0x08); Setvect(0x08,new); Keep(0,1000); } Void interrupt new (){ *scr=64; (*old)(); }

14. New Routine Original Routine Interrupt Interception

15. Memory Mapped Isolated I/O

16. IN M I/O P OUT Isolated I/O

17. Memory Mapped I/O MOV M I/O P MOV

18. Memory Mapped I/O ON Monitor B8OO:0002 B8OO:0003 B8OO:0000 B8OO:0001 Low Byte = ASCII CODE High Byte =Attribute Byte

19. Memory Mapped I/O ON Monitor fore color Blink Back Color Color Bold Low Byte = Ascii Code High Byte = Attribute Byte

20. unsigned int far *scr=0xb8000000; void main() { (*scr)=0x0756; (*(scr+1))=0x7055; }