ISL12027_10 Datasheet, PDF (15/28 Pages) Intersil Corporation – Real Time Clock/Calendar with EEPROM

ISL12027, ISL12027A
There are two alarm operation modes: Single Event and
periodic Interrupt Mode:
1. Single Event Mode is enabled by setting the AL0E or
AL1E bit to “1”, the IM bit to “0”, and disabling the
frequency output. This mode permits a one-time match
between the alarm registers and the RTC registers. Once
this match occurs, the AL0 or AL1 bit is set to “1”. Once
the AL0 or AL1 bit is read, this will automatically reset it.
Both Alarm registers can be set at the same time to
trigger alarms. Polling the SR will reveal which alarm has
been set.
2. Interrupt Mode (or “Pulsed Interrupt Mode” or PIM) is
enabled by setting the AL0E or AL1E bit to “1” the IM bit
to “1”, and disabling the frequency output. If both AL0E
and AL1E bits are set to 1, then only the AL0E PIM alarm
will function (AL0E overrides AL1E). This means that
once the interrupt mode alarm is set, it will continue to
alarm for each occurring match of the alarm and present
time. This mode is convenient for hourly or daily
hardware interrupts in microcontroller applications such
as security cameras or utility meter reading. Interrupt
Mode CANNOT be used for general periodic alarms,
however, since a specific time period cannot be
programmed for interrupt, only matches to a specific time
of day. The interrupt mode is only stopped by disabling
the IM bit or the Alarm Enable bits.
Writing to the Alarm Registers
The Alarm Registers are non-volatile but require special
attention to insure a proper non-volatile write takes place.
Specifically, byte writes to individual registers are good for all
but registers 0006h and 0000Eh, which are the DWA0 and
DWA1 registers, respectively. Those registers will require a
special page write for non-volatile storage. The
recommended page write sequences are as follows:
1. 16-byte page writes: The best way to write or update the
Alarm Registers is to perform a 16-byte write beginning at
address 0001h (MNA0) and wrapping around and ending
at address 0000h (SCA0). This will insure that
non-volatile storage takes place. This means that the
code must be designed so that the Alarm0 data is written
starting with Minutes register, and then all the Alarm1
data, with the last byte being the Alarm0 Seconds (the
page ends at the Alarm1 Y2k register and then wraps
around to address 0000h).
Alternatively, the 16-byte page write could start with
address 0009h, wrap around and finish with address
0008h. Note that any page write ending at address
0007h or 000Fh (the highest byte in each Alarm) will not
trigger a non-volatile write, so wrapping around or
overlapping to the following Alarm's Seconds register is
advised.
2. Other non-volatile writes: It is possible to do writes of
less than an entire page, but the final byte must always
be addresses 0000h through 0004h or 0008h though
000Ch to trigger a non-volatile write. Writing to those
blocks of 5 bytes sequentially, or individually, will trigger a
non-volatile write. If the DWA0 or DWA1 registers need to
be set, then enough bytes will need to be written to
overlap with the other Alarm register and trigger the
non-volatile write. For Example, if the DWA0 register is
being set, then the code can start with a multiple byte
write beginning at address 0006h, and then write 3 bytes
ending with the SCA1 register as follows:
Addr Name
0006h DWA0
0007h Y2K0
0008h SCA1
If the Alarm1 is used, SCA1 would need to have the correct
data written.
Power Control Operation
The power control circuit accepts a V_DD and a V_BAT input.
Many types of batteries can be used with Intersil RTC
products. For example, 3.0V or 3.6V Lithium batteries are
appropriate, and battery sizes are available that can power
an Intersil RTC device for up to 10 years. Another option is
to use a SuperCap for applications where V_DD is interrupted
for up to a month. See “Application Section” on page 22 for
more information.
There are two options for setting the change-over conditions
from V_DD to Battery backup mode. The BSW bit in the PWR
register controls this operation.
Option 1 - Standard Mode: Set “BSW = 0” (default for
ISL12027A)
Option 2 - Legacy/Default Mode: Set “BSW = 1” (default for
ISL12027)
TABLE 6. V_BAT TRIP POINT WITH DIFFERENT BSW SETTING
BSW BIT
V_BAT TRIP
POINT (V)
POWER CONTROL SETTING
0
2.2
Standard Mode (ISL12027A)
1
0
Legacy Mode (ISL12027)
Note that applications that have V_BAT > V_DD will require
theISL12027A (standard mode) for proper start-up. The I²C
bus may or may not be operational during battery backup;
that function is controlled by the SBIB bit. That operation is
covered after the power control section.
OPTION 1 - STANDARD POWER CONTROL MODE
(ISL12027A)
In the Standard mode, the supply will switch over to the
battery when V_DD drops below V_TRIP or V_BAT, whichever is
lower. In this mode, accidental operation from the battery is
prevented since the battery backup input will only be used
when the V_DD supply is shut off.
To select Option 1, BSW bit in the Power Register must be
set to “BSW = 0”. A description of power switchover follows.
15
FN8232.8
August 12, 2010