V22.0201.002, Machine Organization I, Professor Yap
Fall 1997

NOTES ON MOUSE and PORTS

CONTENTS

• Introduction
• Table of Mouse Interrupt Functions (INT 33h)
• Mouse Cursor
• Bottom of page

INTRODUCTION

• INT 33h is used for manipulating the mouse. Note that the mouse is available in both graphics and text modes.
• IN/INS and OUT/OUTS are for accessing ports.
• The mouse in controlled by a software interface called a mouse driver which is usually installed by an entry in the file CONFIG.SYS or AUTOEXEC.BAT. (I have not found the corresponding location for this in WIN95 or WINNT.)
• Basic Terminology for mouse:

  pixel:

  smallest addressable element on screen. In text mode 03, there 8 pixels stored in a video byte.

  mouse pointer:

  in text mode, this is a flashing block, but in reverse video. In graphics mode, this is an arrowhead. In text mode, this is usually a blinking (character size) rectangle.

  mickey:

  a unit of measure for movement of mouse, approx. 1/200 of an inch.

  mickey count:

  number of mickeys the mouse ball rolls (either horizontally or vertically). The mouse driver converts this to number of pixels.

  threshhold speed:

  the speed in mickeys/second that the mouse must move to double the speed of the pointer on the screen. Default is 64 mickeys/s.

• Mouse interrupt have the form:

  	mov ax,fcn	; fcn=mouse function number
  	...
  	int 33h
  	

  Note that this is unlike other int's which use only the ah (not ax) register for specifying function number. The first mouse instruction a program issues should be fcn=00h. This initializes the interface between the mouse driver and the program. This is usually done only once. Next it should issue fcn=01h, which cause the mouse pointer to appear.
• Mouse functions from int 33h: Here is function fcn=0, which initializes the mouse. It should be the first function to call if you ever use the mouse.

  RETURNS AX=0000h if no mouse support available, AX=FFFFh otherwise.
  RETURNS BX=number of mouse buttons available (if AX=FFFFh).
  Other actions:

  • places mouse at center of screen
  • makes mouse invisible
  • sets mouse pointer display page to 0
  • sets mickey-to-pixel ratios (horizontal ratio is 8:8, vertical ratio is 16:8). Thus the mouse pointer moves half as fast in the vertical direction.
  • sets hori. and vert. limits for pointers to their max and min values.
  • sets double-speed threshhold to 64 mickeys/s.
  • enables light pen emulation mode.
  In a table below we show some common functions (fcns), but see helppc for the complete list.
• Here is a program that exercises the basic mouse functions,

MOUSE INTERRUPT FUNCTIONS

MOUSE CURSOR

The SCREEN MASK is AND'ed with the display screen. The CURSOR MASK is OR'ed with the result. Thus we have the following behaviour:

 
        SCREEN MASK     CURSOR MASK     RESULTING SCREEN BIT
            0               0                   0
            0               1                   1
            1               0               unchanged
            1               1                inverted
 	

                mov ax, 9
                mov bx, -1      ; default hot spot is past arrow tip
                mov cx, -1
                mov dx, offset default
                                ; we assume ES is properly set up already
                int 33h
                ;
                default:
                ; screen mask ---
                  db    0011111111111111b
                  db    0001111111111111b
                  db    0000111111111111b
                  db    0000011111111111b
                ;
                  db    0000001111111111b
                  db    0000000111111111b
                  db    0000000011111111b
                  db    0000000001111111b
                ;
                  db    0000000000111111b
                  db    0000000111111111b
                  db    0001000011111111b
                  db    0011000011111111b
                ;
                  db    1111100001111111b
                  db    1111100001111111b
                  db    1111110000111111b
                  db    1111111111111111b
                ;
                ; cursor mask ---
                  db    0000000000000000b
                  db    0100000000000000b
                  db    0110000000000000b
                  db    0111000000000000b
                ;
                  db    0111100000000000b
                  db    0111110000000000b
                  db    0111111000000000b
                  db    0111111100000000b
                ;
                  db    0111111110000000b
                  db    0111111111000000b
                  db    0111110000000000b
                  db    0100011000000000b
                ;  
                  db    0000011000000000b
                  db    0000001100000000b
                  db    0000001100000000b
                  db    0000000000000000b