INT 1aH 06H: Set Real-Time Clock Alarm
Expects: AH 06H
CH hours, in BCD▲
CL minutes, in BCD
DH seconds, in BCD
Returns: AH 0
CF NC (0) no error
CY (1) alarm already operating
Info: Sets the BIOS to invoke INT 4aH at the specified time.
You must supply an INT 4aH handler if you want to get control at
the specified time (and avoid a system crash!). The vector for
INT 4aH is at 0000:0128H.
Only one alarm may be set at a time. If an alarm is already
active, this returns with the Carry Flag set and take no action.
Use INT 1aH 07H to cancel a previously-set alarm.
Note: Using this as described is quite unusual. A more common
technique is to patch a TSR into INT 08H and keep an eye on the
system time. That way you can set up multiple timers, etc.
See Also: INT 1aH (BIOS Time I/O)