Int 15 Fn 41  - System - Wait On External Event (convertible And Some Oth  [B]

   AH = 41h
   AL = condition type (see #0389)
   BH = condition compare or mask value
   BL = timeout value times 55 milliseconds
       00h means no timeout
   DX = I/O port address if AL bit 4 set
   ES:DI -> user byte if AL bit 4 clear

Return: after event or timeout occurs

Note:  call AH=C0h and examine bit 3 of feature byte 1 to determine whether
     this function is supported

See Also: AH=83h,AH=86h,AH=C0h

Bitfields for external event wait condition type:
Bit(s) Description (Table 0389)
 0-2   condition to wait for
   0 any external event
   1 compare and return if equal
   2 compare and return if not equal
   3 test and return if not zero
   4 test and return if zero
 3 reserved
 4 1=port address, 0=user byte
 5-7   reserved