ISL12022MA_10 Datasheet, PDF (28/29 Pages) Intersil Corporation – Low Power RTC with Battery Backed SRAM, Integrated ±5ppm Temperature Compensation and Auto Daylight Saving

ISL12022MA
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 ISL12022MA.
TABLE 26. DST EXAMPLE
VARIABLE
VALUE REGISTER
Month Forward and April
15h
DST Enable
Week and Day Forward 1st Week and
16h
and select Day/Week, Sunday
not Date
Date Forward
Not used
17h
Hour Forward
2am
18h
Month Reverse
October
19h
Week and Day Reverse Last Week
and select Day/Week, and Sunday
not Date
1Ah
Date Reverse
Not used
1Bh
Hour Reverse
2am
1Ch
VALUE
84h
48h
00h
02h
10h
78h
00h
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”.
Device Handling Precautions
The ISL12022MA contains a quartz crystal and requires
special handling during PC board assembly. Excessive
shock and vibrations should be avoided, especially with
automated handling equipment (see “Absolute Maximum
Ratings” on page 5 for shock and vibration). Avoid
dropping onto hard surfaces, placing rubber floor mats in
assembly areas will greatly reduce the risk of damage.
PCB panel routing should be monitored to avoid
generating vibrations at hormonics of the crystal
frequency (32kHz). If possible, router speed should be
adjusted to mitigate this risk.
Ultrasound cleaning is not advisable as it subjects the
crystal to resonance and possible failure. Units subject to
shock, vibration or ultrasound may sustain crystal
failures in one of many modes, all of which will affect
oscillator frequency accuracy or cause oscillator failure.
See also Note 6 on page 5 in the specifications tables,
which pertains to solder reflow effects on oscillator
accuracy. Note that overheating the package, in excess
of +260° for >30 sec, will cause damage to the crystal
seal and compromise oscillator accuracy.
Revision History
The revision history provided is for informational purposes only and is believed to be accurate, but not warranted. Please go to
web to make sure you have the latest Rev.
DATE
REVISION
CHANGE
7/1/10
FN7575.1
In the “Device Handling Precautions” on page 28, changed the max reflow temperature from
“+280°C” to “+260° for >30 sec”
6/1/10
FN7575.0 Initial Release.
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28
FN7575.1
July 9, 2010