Apple II
Technical Notes
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                                                  Developer Technical Support


Mouse
#3:    Mode Byte of the SetMouse Routine

Revised by:    Matt Deatherage                                  November 1988
Revised by:    Rilla Reynolds                                   November 1985

This Technical Note explains the results of turning the mouse on and off 
through the mode byte of the SetMouse routine. 
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What Turning the Mouse Off Does

In the description of SetMouse and the mouse mode, the low-order bit of the 
mouse mode is said to control mouse off and mouse on.  This terminology is 
somewhat misleading.  When this bit is set to 0, the mouse is off only in the 
following respects:

1.    The mouse position is not tracked; any mouse motion is ignored.
2.    ReadMouse calls do not update the status byte or the screen holes, 
      except on the IIGS, where ReadMouse always functions the same, 
      regardless of mouse on or mouse off.
3.    Button and movement interrupts are not generated, regardless of 
      the other mouse mode bits.  Pure VBL interrupts can still be 
      generated, however, if bit 3 is set.


What Turning the Mouse Off Does Not Do

Other mouse functions will continue to work as usual when the mouse is off.  
PosMouse and ClearMouse will change the mouse position, ClampMouse will set 
new clamp values, etc.  In particular:

1.    Turning the mouse off and on with the mode byte does not reset any 
      mouse values, including position.  The mouse position retains the 
      last values it had before the mouse was turned off until it is 
      turned on again.
2.    A mode byte of $08 (mouse off but VBL interrupt on) will generate 
      VBL interrupts.


Further Reference
o    Apple IIGS Firmware Reference
o    Apple IIe Technical Reference Manual
o    Apple IIc Technical Reference Manual, Second Edition