Int 1A Fn 06  - Time - Set Alarm (at,xt286,ps)                             [B]

   AH = 06h
   CH = hour (BCD)
   CL = minutes (BCD)
   DH = seconds (BCD)

Return: CF set on error (alarm already set or clock stopped for update)
   CF clear if successful

Notes: the alarm occurs every 24 hours until turned off, invoking INT 4A each
     time
   the BIOS does not check for invalid values for the time, so the CMOS
     clock chip's "don't care" setting (any values between C0h and FFh)
     may be used for any or all three parts.  For example, to create an
     alarm once a minute, every minute, call with CH=FFh, CL=FFh, and
     DH=00h.

See Also: AH=07h,AH=0Ch,INT 4A"SYSTEM"