Int 21 Fn 31  - Dos 2+ - Terminate And Stay Resident                       [D]

   AH = 31h
   AL = return code
   DX = number of paragraphs to keep resident

Return: never

Notes: the value in DX only affects the memory block containing the PSP;
     additional memory allocated via AH=48h is not affected
   the minimum number of paragraphs which will remain resident is 11h
     for DOS 2.x and 06h for DOS 3.0+
   most TSRs can save some memory by releasing their environment block
     before terminating (see #1066 at AH=26h,AH=49h)
   any open files remain open, so one should close any files which will
     not be used before going resident; to access a file which is left
     open from the TSR, one must switch PSP segments first (see AH=50h)

See Also: AH=00h,AH=4Ch,AH=4Dh,INT 20,INT 22,INT 27