isl12022m Intersil Corporation, isl12022m Datasheet - Page 26

• Manufacturer Part Number: isl12022m
• Description: Real Time Clock With Embedded Crystal, ??5ppm Accuracy
• Manufacturer: Intersil Corporation

the value for BETA is locked and cannot be changed with a
write. It is still a good idea to do the bit masking when doing
TSE bit changes, though.
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.
An example setup for the ISL12022M follows.
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
26
15h
16h
17h
18h
19h
1Ah
1Bh
1Ch
REGISTER
84h
48h
00h
02h
10h
78h
00h
02h
VALUE
ISL12022M
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”.
December 18, 2008
FN6668.4