INT 1A - TIME - GET REAL-TIME CLOCK TIME (AT,XT286,PS)
        AH = 02h
Return: CF clear if successful
            CH = hour (BCD)
            CL = minutes (BCD)
            DH = seconds (BCD)
            DL = daylight savings flag (00h standard time, 01h daylight time)
        CF set on error (i.e. clock not running or in middle of update)