Int 15 Fn 5101  - System - Later Ps/2s - Expansion Unit, Return Configura  [B]

   AX = 5101h

Return: CF set if successful
       AH = 00h
       AL = current configuration number
       00h system unit only
       FFh configuration not recognized
       BX = status flag
       bits 0-14: reserved
       bit 15: additional data is available (location TBD)
   CF clear on error
       AH = status
       01h expansion unit is not present
       86h function not supported

Note:  CF convention is the reverse of the standard convention for this
     interrupt.  (Perhaps a typo in the IBM BIOS Tech Ref?)