
Click above to get retro games delivered to your door ever month!
X-Hacker.org- BIOS ref. - <b>int 1ah, 06h set real-time clock alarm many</b>
[<<Previous Entry] [^^Up^^] [Next Entry>>] [Menu] [About The Guide]
Int 1Ah, 06h Set Real-Time Clock Alarm many
Sets the time at which the computer will issue an alarm by calling
Int 4Ah.
Entry AH = 06h
CH = Hours (BCD)
CL = Minutes (BCD)
DH = Seconds (BCD)
Return CF Set if clock not operating or alarm already set;
else cleared
------------------------------------------------------------------
All dates are in Binary Coded Decimal (BCD). For example, June 1,
1985 will be set as CX = 1985; DX = 0601.
The real-time clock is the clock that runs even when the computer
is turned off. A CMOS battery is used so that, even while the
computer is off, the date, time, and alarm time are maintained.
This service is available only for ATs, XT-286s, and PC
Convertibles. Previous machines will report unpredictable results
(including the state of the Carry Flag).
After this service is executed, an Int 4Ah will be generated as
soon as the hour, minute, and second specified match the time on
the real-time clock date. It is up to the programmer to install an
interrupt handler for Int 4Ah before calling this service
The alarm interrupt (Int 4Ah) will continue to occur every 24
hours at the specified time until it is reset via Service 07h
(Reset Real-Time Clock Alarm). Only one alarm time can be active
at a time.
Because the real-time clock is updated even if the computer is
turned off, the alarm time set via this service will remain active
even after the computer is turned off (of course, the alarm won't
be generated while the computer is off).
Setting the real-time clock date will not affect the system date.
This is because the real-time clock is read once upon system
startup, updating the system timer. All other references to date
use the system timer. If either the real-time clock date is
changed (via Service 05h) or the system timer is changed (via
Service 01h), the other date is not changed accordingly.
Even though the system is using the system timer for date
information, both the real-time clock and the system timer are
updated continuously.
See Also: Int 1Ah, 07h Int 1Ah, 08h Int 1Ah, 09h
Online resources provided by: http://www.X-Hacker.org --- NG 2 HTML conversion by Dave Pearson