INT 15h,  41h (65)       Wait for External Event                  Convertible

This service waits for a specified status change after an external
event. The external event can be an interrupt or the DMA controller.
While waiting for the specific status, the system clocks are stopped
in order to conserve battery power. This service is available only for
the PC Convertible.

On entry:      AH         41h
AL         Event Type code (see below)
BH         Condition compare or mask value
BL         Time-out (in units of 55 ms); 0 means no
time-out
ES:DI      Pointer to user byte for event determination
(if AL is 01h-04h)
DX         I/O Port Address for event determination (if
AL is 11h-14h)

Returns:       Carry      0 - external event occurred
1 - time-out

                                                                          

  AL -- Event Type Code (AL)

00h            Return after any event has occurred
01h            Compare value; return if equal
02h            Compare value; return if not equal
03h            Test bit; return if non-0
04h            Test bit; return if 0

Event Type Codes 11h-14h are the same as 01h-04h, except the event
determination is coming from the I/O Port Address in DX, instead of
the user byte specified by ES:DI.

If the event type is 01h-02h or 11h-12h, then the byte signaling the
event determination is compared (using the CMP instruction) against
BH. If the event type is 03h-04h or 13h-14h, then the byte signaling
the event determination is tested (using the TEST instruction) against
BH.

Notes:         This service is available only for the PC
Convertible.


INT 15h, 41h (65) Wait for External Event Convertible