INT 15 - SYSTEM - WAIT ON EXTERNAL EVENT (CONVERTIBLE and some others)
	AH = 41h
	AL = condition type (see #00463)
	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
SeeAlso: AH=83h,AH=86h,AH=C0h


Bitfields for external event wait condition type:
Bit(s)	Description	(Table 00463)
 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