ISL12022M_10 Datasheet, PDF (28/31 Pages) Intersil Corporation – Low Power RTC with Battery Backed SRAM,Integrated ±5ppm Temperature Compensation and Auto Daylight Saving

ISL12022M
Daylight Savings Time (DST) Example
DST involves setting the forward and back times and
allowing the RTC device to automatically advance the
time or set the time back. This can be done for current
year, and future years. Many regions have DST rules that
use standard months, weeks and time of the day, which
permit a pre-programmed, permanent setting.
Table 26 shows an example setup for the ISL12022M.
TABLE 26. DST EXAMPLE
VARIABLE
VALUE REGISTER VALUE
Month Forward and
DST Enable
April
15h
84h
Week and Day Forward 1st Week and 16h
48h
and select Day/Week, Sunday
not Date
Date Forward
not used
17h
00h
Hour Forward
2am
18h
02h
Month Reverse
October
19h
10h
Week and Day Reverse Last Week 1Ah
78h
and select Day/Week, and Sunday
not Date
Date Reverse
not used
1Bh
00h
Hour Reverse
2am
1Ch
02h
The Enable bit (DSTE) is in the Month forward register,
so the BCD value for that register is altered with the
additional bit. The Week and Day values along with
Week/Day vs Date select bit is in the Week/Day register,
so that value is also not straight BCD. Hour and Month
are normal BCD, but the Hour doesn’t use the MIL bit
since Military time PM values are already discretely
different from AM/PM time PM values. The DST reverse
setting utilizes the option to select the last week of the
month for October, which could have 4 or 5 weeks but
needs to have the time change on the last Sunday.
Note that the DSTADJ bit in the status register monitors
whether the DST forward adjustment has happened.
When it is “1”, DST forward has taken place. When it is
“0”, then either DST reverse has happened, or it has
been reset either by initial power-up or if the DSTE bit
has been set to “0”.
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FN6668.7
June 4, 2010