INT 1Ah,  05h (5)        Set Real-Time Clock Date                        many

Sets the date on the computer's real-time clock.

On entry:      AH         05h
CH         Century (19 or 20) (BCD)
CL         Year (BCD)
DH         Month (BCD)
DL         Day (BCD)

                                                                          

Notes:         All dates are in Binary Coded Decimal (BCD). For
example, January 15, 1987 will be set as CX = 1987;
DX = 0115.

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).

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 this service) or the system timer is changed
(via Service 01h), the other date is not changed
accordingly.

Even though the system uses the system timer for
date information, both the real-time clock and the
system timer are updated continuously.

See also: INT 1Ah, 04h
See also: INT 1Ah, 0Bh

INT 1Ah, 05h (5) Set Real-Time Clock Date many