Confused about C program with assembly

[Ananthu]

Hi

In my college they have given me the following codings for implementing linker function.

Codings:

#include<stdio.h>
#include<conio.h>
void cursoron();
void cursoroff();
void main()
{
clrscr();
printf("LINKER\n\n");
printf("Cursor off state\n");
cursoroff();
getch();
printf("\nCursor on state\n");
cursoron();
getch();
printf("\nCursor off state\n");
cursoroff();
getch();
printf("\nCursor on state\n");
cursoron();
getch();
}
 
void cursoron()
{
 asm MOV AH,3;
 asm XOR BX,BX;
 asm INT 0X10;
 asm XOR CH,0X3F;
 asm MOV AH,1;
 asm INT 0X10;
}
 
void cursoroff()
{
 asm MOV AH,3;
 asm XOR BX,BX;
 asm INT 0X10;
 asm OR CH,0X3F;
 asm MOV AH,1;
 asm INT 0X10;
}

Output:

Cursor off state

Cursor on state
-

Cursor off state

Cursor on state
-


- indicates blinking cursor in output.
I know the assembly language codings only a little bit. Can you please explain me what each assembly language statements are doing for cursoron() function alone so that i can understand cursoroff() function also.

I know the meaning of MOV,XOR,INT,OR etc.. But what is the purpose of moving values 3,1 in A register before and after cursor on/off stage and why we are clearing BX register,why we are moving 0X3F in CH register. What actually they do.

Can u please explain me...

[Cucumber]

It is imperative to have the interruption's documentation prior to coding anything related to sowftare interruptions.

In your case, you need to take a look to this link
http://www.ctyme.com/intr/int-10.htm

There you can lookup what does the software interruption 0x10 do when you "feed" it AH = 3 and so on.

For instance, AH=3 means "VIDEO - GET CURSOR POSITION AND SIZE", AH=1 means "VIDEO - SET TEXT-MODE CURSOR SHAPE", and so on,

Just click and read.