1. Lecture 16

2. Example: #include<BIOS.H> #include<DOS.H> char ch1, ch2;
void initialize (int pno) {
_AH=0;
_AL=0x57;
_DX=pno;
geninterrupt(0x14); }

3. char receivechar (int pno){
char ch;
_DX = pno;
_AH = 2;
geninterrupt (0x14);
ch = _AL;
return ch; }

4. void sendchar (char ch, int pno){
_DX = pno;
_AH = 1;
_AL = ch;
geninterrupt (0x14); }
unsigned int getcomstatus (int pno)
unsigned int temp;
_AH = 03;
*((char*)(&temp)) = _AL;
*(((char*)(&temp)) + 1) = _AH;
return temp;

5. void main() {
while(1) {
i = getcomstatus (0);
if (((*(((char*)(&i)) + 1)&0x20) == 0x20) && (kbhit()))
ch1 = getche();
sendchar (ch1, 0); }
if ((*(((char*)(&i)) +1) & 0x01) == 0x01) {
ch2 = receivechar (0);
putch (ch2);
if ((ch1 == 27) || (ch2 ==27))
break;

6. Line Control Register 7 6 5 4 3 2 1 Word Length 0 Load THR 00 = 5 BITS
Word Length
0 Load THR
1Load Divisor Value
00 = 5 BITS
01 = 6 BITS
10 = 7 BITS
11 = 8 BITS
Stop Communication =1
Resume Communication =0
Length of Stop BITS
0 = one BIT
1 =1-5 for 5 bit Word
Constant Parity
0 =NO constant Parity
1 =Constant Parity
0 if bit 4 =1
1 if bit 4 =0
Parity Check and
generation on
Parity
O = odd
1 = Even.

7. #include <dos.h>
#include <bios.h>
void initialize (unsigned int far *com) {
outportb ( (*com)+3, inport ((*com)+3) | 0x80);
outportb ( (*com),0x80);
outportb( (*com) +1, 0x01);
outportb ( (*com)+3, 0x1b); }
void SelfTestOn(unsigned int far * com)
outportb((*com)+4,inport((*com)+4)|0x10);

8. void SelfTestOff(unsigned int far * com){
outportb( (*com)+4, inport((*com)+4) & 0xEf); }
void writechar( char ch, unsigned int far * com)
while ( !((inportb((*com)+5) & 0x20) == 0x20));
outport(*com,ch);
char readchar( unsigned int far *com)
while (!((inportb((*com)+5) & 0x01)==0x01));
return inportb(*com);

9. unsigned int far *com=(unsigned int far*) 0x00400000;
void main () {
char ch = 0; int i = 1;int j= 1;
char ch2='A';
initialize( com);
SelfTestOn(com);
clrscr();
while (ch!=27)
if (i==80)
j++;
i=0; }

10. if (j==13)
j=0;
gotoxy(i,j);
ch=getche();
writechar(ch,com);
ch2=readchar(com);
gotoxy(i,j+14);
putch(ch2);
i++; }
SelfTestOff (com);

11. hello how r u ? whats new about systems programming?

12. #include <dos.h>
#include <bios.h>
void initialize (unsigned int far *com) {
outportb ( (*com)+3, inport ((*com)+3) | 0x80);
outportb ( (*com),0x80);
outportb( (*com) +1, 0x01);
outportb ( (*com)+3, 0x1b); }
void SelfTestOn(unsigned int far * com)
outportb((*com)+4,inport((*com)+4)|0x18);

13. void SelfTestOff(unsigned int far * com) {
outportb( (*com)+4, inport((*com)+4) & 0xE7); }
void writechar( char ch, unsigned int far * com)
//while ( !((inportb((*com)+5) & 0x20) == 0x20));
outport(*com,ch);
char readchar( unsigned int far *com)
//while (!((inportb((*com)+5) & 0x01)==0x01));
return inportb(*com);

14. unsigned int far *com=(unsigned int far*) 0x00400000;
unsigned char far *scr=(unsigned char far*) 0xB ;
int i =0,j=0;char ch;int k;
void interrupt (*oldint)();
void interrupt newint();
void main () {
initialize(com);
SelfTestOn(com);
oldint = getvect(0x0c);
setvect(0x0c,newint);
outport((*com)+1,1);
outport(0x21,inport(0x21)&0xEF);
keep(0,1000); }

15. void interrupt newint(){
ch= readchar(com);
if (i==80)
j++;
i=0; }
if (j==13)
j=0;
k = i*2+(j+14)*80*2;
*(scr+k)=ch;
i++;
outport(0x20,0x20);

16. C:\>DEBUG -o 3f8 41 -o 3f8 42 -o 3f8 56 -o 3f8 55 -q C:\>

17. #include <bios. h> #include <dos. h> void interrupt (
#include <bios.h> #include <dos.h> void interrupt (*oldint)(); void interrupt newint(); unsigned char far *scr= (unsigned char far *)0xB ; void initialize (unsigned int far *com) { outportb ( (*com)+3, inport ((*com)+3) | 0x80); outportb ( (*com),0x80); outportb( (*com) +1, 0x01); outportb ( (*com)+3, 0x1b); }

18. void main (void)
{ oldint = getvect(0x0C); setvect (0x0C,newint);
initialize (*com);
outport ((*com)+4, inport ((*com)+4) | 0x08); outport (0x21,inport (0x21)&0xEF); outport ((*com) + 1, 1); keep(0,1000); }
void interrupt newint () {
*scr = inport(*com); outport (0x20,0x20);