Int 0A  P - CPU-generated (80286+) - Invalid Task State Segment            [C]

Desc:  automatically called during a task switch if the new TSS specified by
     the task gate is invalid for any of the following reasons:
       TSS limit is less than 43 (80286) or 103 (80386/80486)
       LDT selector invalid or segment not present
       null SS selector, or SS selector outside LDT/GDT limit
       stack segment is read-only
       stack segment DPL differs from new CPL, or RPL <> CPL
       CS selector is outside LDT/GDT limit or not code
       non-conforming code segment's DPL differs from CPL
       conforming code segment's DPL > CPL
       DS/ES selectors outside LDT/GDT limit or not readable segments

Note:  the handler must use a task gate in order to have a valid TSS under
     which to execute; it must also reset the busy bit in the new TSS

See Also: INT 0B"CPU"