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)
_DX = (unsigned int) st1;

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

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. Keyboard Status Word 7 6 5 4 3 2 1 40:17H Insert key Caps Lock Key
40:17H
Insert key
Caps Lock Key
Num Lock key
Scroll lock key
Right Shift key
Left Shift Key
Ctrl Key
Alt Key
Keyboard Status Word

13. #include <dos.h>
void Interrupt (*old)();
void Interrupt new();
Char far *scr=(char far* ) 0x ;
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. Isolated I/O M P
I/O IN
OUT

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 X
Blink
Back Color
Color
Bold
000
Black
100
Red
010
Green
001
Blue
111
White
Low Byte = Ascii Code
High Byte = Attribute Byte

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