INT 1Ah,  03h (3)        Set Real-Time Clock Time                        many

Sets the time for the computer's real-time clock.

On entry:      AH         03h
CH         Hours (BCD)
CL         Minutes (BCD)
DH         Seconds (BCD)
DL         1 if daylight saving time option; else 0

Returns:       None


Notes:         All times are in Binary Coded Decimal (BCD). For
example, 9:04.12 am would be set as CX = 0904; DH =

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 will not affect the
system time. This is because the real-time clock is
read once upon system startup, updating the system
timer. All other references to time use the system
timer. If either the real-time clock is changed (via
this service) or the system timer is changed (via
Service 01h), the other clock is not changed

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

See also: INT 1Ah, 01h
See also: INT 1Ah, 02h

INT 1Ah, 03h (3) Set Real-Time Clock Time many