Int 21 Fn 250F  P - Phar Lap 386/dos-extender - Convert Protected-mode Ad  [E]

   AX = 250Fh
   ES:EBX = 48-bit protected-mode address to convert
   ECX = 00000000h or length of data in bytes

Return: CF clear if successful (address < 1MB and contiguous)
       ECX = 32-bit real-mode MS-DOS address
   CF set on error (address >= 1MB or not contiguous)
       ECX = linear address

Note:  this function is also supported by FlashTek X-32VM

See Also: AX=2510h