HelpPC 2.10 Quick Reference Utility Copyright 1991 David Jurgens

          INT 33,18 - Set alternate subroutine call mask and address

       AX = 18h
       DX = offset to function
       CX = user interrupt mask:

               │F-8│7│6│5│4│3│2│1│0│ user interrupt mask in CX
                 │  │ │ │ │ │ │ │ └─── alt key pressed during event
                 │  │ │ │ │ │ │ └──── ctrl key pressed during event
                 │  │ │ │ │ │ └───── shift key pressed during event
                 │  │ │ │ │ └────── right button up event
                 │  │ │ │ └─────── right button down event
                 │  │ │ └──────── left button up event
                 │  │ └───────── left button down event
                 │  └────────── cursor moved
                 └──────────── unused

       - entire mask is set to zero when INT 33,0 is called
       - up to three handlers may be defined with this call
       - mask should be cleared before program exit
       - when handler is called it receives parameters in the following
         registers:

         AX = condition mask causing call
         CX = horizontal cursor position
         DX = vertical cursor position
         DI = horizontal counts
         SI = vertical counts
         DS = mouse driver data segment
         BX = button state:

            │F-2│1│0│
              │  │ └─── left button (1 = pressed)
              │  └──── right button (1 = pressed)
              └────── unused

Esc or Alt-X to exit int 33,18 Home/PgUp/PgDn/End ←↑↓→