Text Mode Cursor

Moving the Cursor with the BIOS

Moving the cursor with the BIOS is through Int 10h with Ah set to 02h. (The general interrupt for screen functions.) These are the registers used:

• AH = 02h
• BH = Display Page (This is usually, if not always, 0.)
• DH = The row
• DL = The column

Then, with a quick call to interrupt 10h, you should have yourself a movable type cursor!

Moving the Cursor without the BIOS

Without access to BIOS calls and functions, moving the cursor requires using video hardware control. Lucky it is a simple procedure.

Note, this quick example ASSUMES 80x25 screen mode.

/* void update_cursor(int row, int col)
 * by Dark Fiber
 */
void update_cursor(int row, int col)
{
   unsigned short position=(row*80) + col;

   // cursor LOW port to vga INDEX register
   outb(0x3D4, 0x0F);
   outb(0x3D5, (unsigned char)(position&0xFF));
   // cursor HIGH port to vga INDEX register
   outb(0x3D4, 0x0E);
   outb(0x3D5, (unsigned char )((position>>8)&0xFF));
}

Keep in mind that in/out to VGA Hardware is a slow operation. So using the hardware registers to remember of the current character location (row, col) is bad practice -- and updating position after each displayed character is poor practice (updating it only when a line/string is complete is wiser and hiding it until a user prompt is required is wisest)

See Also

External Links

• http://www.bookcase.com/library/dos/ints/int10.html
• http://www.arl.wustl.edu/~lockwood/class/cs306/books/artofasm/Chapter_13/CH13-2.html