1. Lecture 22

2. Keyboard writing Protocol
Wait till input buffer is full
Write on buffer
Wait till output buffer is full
Check the acknowledgement byte
Repeat the process if it was previously unsuccessful.

3. 0xF3 Command for writing Typematic rate
Means Typematic rate will be sent in the next byte.

4. Keyboard LEDs 2 1 LED Status byte Scroll Lock Num Lock Caps Lock
Scroll Lock
Num Lock
Caps Lock
LED Control byte = 0xED

5. #include <dos.h>
#include <conio.h>
char st [80];
int SendKbdRate(unsigned char data , int maxtry) {
unsigned char ch;
do{
ch=inport(0x64);
}while (ch&0x02);
outport(0x60,data);
ch = inport(0x64);
}while (ch&0x01);

6. if (ch==0xfa)
{ puts("success\n");
break; }
maxtry = maxtry - 1;
} while (maxtry != 0);
if (maxtry==0)
return 1;
else
return 0;

7. void main () {
//clrscr();
SendKbdRate(0xf3,3);
SendKbdRate(0x7f,3);
gets(st);
SendKbdRate(0,3); }

8. #include <bios.h>
#include <dos.h>
char st [80];
unsigned char far *kbd =
(unsigned char far *) 0x ;
int SendKbdRate(unsigned char data , int maxtry) {
unsigned char ch;
do{
ch=inport(0x64);
}while (ch&0x02);
outport(0x60,data);

9. do{
ch = inport(0x64);
}while (ch&0x01);
ch=inport(0x60);
if (ch==0xfa)
{ puts("success\n");
break; }
maxtry = maxtry - 1;
} while (maxtry != 0);
if (maxtry==0)
return 1;
else
return 0;

10. void main () {
//clrscr();
SendKbdRate(0xed,3);
SendKbdRate(0x7,3);
puts("Enter a string ");
gets(st);
*kbd=(*kbd )|0x70; }

11. DMA Controller
Main Memory
I/O
Processor
DMA

12. DMA Interfacing