isl12020m Intersil Corporation, isl12020m Datasheet - Page 27

• Manufacturer Part Number: isl12020m
• Description: Real Time Clock With Embedded Crystal, ?5ppm Accuracy
• Manufacturer: Intersil Corporation

Temperature Compensation Operation
The ISL12020M temperature compensation feature needs to
be enabled by the user. This must be done in a specific order
as follows.
Note that every time the BETA register is written with the
TSE bit = 1, a temperature compensation cycle is instigated
and a new correction value will be loaded into the
FATR/FDTR registers (if the temperature changed since the
last conversion).
Also note that registers 0Bh and 0Ch, the ITR0 and ALPHA
registers, should not be changed. If they must be written be
sure to write the same values that are recalled from initial
power-up. The ITR0 register may be written if the user
wishes to re-calibrate the oscillator frequency at room
temperature for aging or board mounting. The original
recalled value can be re-written if desired after testing.
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
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1. Read register 0Dh, the BETA register. This register
2. Bit 7 of the BETA register is the master enable control for
3. Bits 5 and 6 of the BETA register control temperature
4. Write back to register 0Dh making sure not to change the
contains the 5-bit BETA trimmed value, which is
automatically loaded on initial power-up. Mask off the
5LSB’s of the value just read.
temperature sense operation. Set this to “1” to allow
continuous temperature frequency correction. Frequency
correction will then happen every 60s with V
compensation in battery-backup mode (see Table 15 on
page 18). Set the values for the operation desired.
5 LSB values, and include the desired compensation
control bits.
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27
DD
applied.
ISL12020M
standard months, weeks and time of the day, which permit a
pre-programmed, permanent setting.
An example setup for the ISL12022 is in Table 26.
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”.
Month Forward and DST
Enable
Week and Day Forward
and select Day/Week, not
Date
Date Forward
Hour Forward
Month Reverse
Week and Day Reverse
and select Day/Week, not
Date
Date Reverse
Hour Reverse
VARIABLE
TABLE 26. DST EXAMPLE
April
1st Week and
Sunday
not used
2am
October
Last Week and
Sunday
not used
2am
VALUE
15h
16h
17h
18h
19h
1Ah
1Bh
1Ch
REGISTER
January 15, 2009
84h
48h
00h
02h
10h
78h
00h
02h
VALUE
FN6667.2