Int 1A Fn 81  - PCmcia Socket Services - Register Status Change Callback   [X]

   AH = 81h
   DS:DX -> callback routine (see below) or 0000h:0000h to disable

Return: CF clear if successful
       AH destroyed
   CF set on error
       AH = error code (see AH=80h"PCMCIA")

Note:  the callback will be invoked on any socket changes whose notification
     has not been disabled with the status change enable mask; it may be
     invoked either while processing a hardware interrupt from the adapter
     or while processing the following Socket Services request

See Also: AH=80h"PCMCIA",AH=82h"PCMCIA"

Callback routine invoked with:
   AL = adapter number
   BH = status change interrupt enable mask (see below)
   BL = socket number
   DH = current socket status (see below)
   DL = current card status (see below)

Return: all registers preserved

Notes: the callback may be invoked during a hardware interrupt, and may not
     call on Socket Services
   the callback will be invoked once for each socket with a status change

Bitfields for status change enable mask:
 bits 0,1 reserved (0)
 bit 2 ejection request
 bit 3 insertion request
 bit 4 battery dead change
 bit 5 battery warning change
 bit 6 ready change
 bit 7 card detect change

Bitfields for current socket status:
 bit 0 reserved (0)
 bit 1 card locked
 bit 2 card ejection request pending
 bit 3 card insertion request pending
 bit 4 card ejection complete
 bit 5 card insertion complete
 bit 6 reserved (0)
 bit 7 card changed

Bitfields for current card status:
 bit 0 write protected
 bits 1-3 reserved (0)
 bit 4 battery voltage detect 1 (battery dead)
 bit 5 battery voltage detect 2 (battery warning)
 bit 6 ready
 bit 7 card detect