Int 14 Fn 8B  - Comm-drv V14.0 - Set User Interrupt Routine                [S]

   AH = 8Bh
   CX = bitmask of interrupt to process
       00h = deinstall
   BX:DI -> DWORD containing address of function to be called

Return: AH bit 7 clear if successful
   AH bit 7 set on error