±5ppm, I2C Real-Time Clock with SRAM ( 23 Page)
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C Real-Time Clock with SRAM
The device contains two time-of-day/date alarms.
Alarm 1 can be set by writing to registers 07h–0Ah.
Alarm 2 can be set by writing to registers 0Bh–0Dh.
. The alarms can be programmed (by the
alarm enable and INTCN bits in the Control register)
to activate the INT/SQW output on an alarm match
condition. Bit 7 of each of the time-of-day/date alarm
registers are mask bits
When all the mask
bits for each alarm are logic 0, an alarm only occurs
when the values in the timekeeping registers match the
corresponding values stored in the time-of-day/date
alarm registers. The alarms can also be programmed
to repeat every second, minute, hour, day, or date.
shows the possible settings. Configurations
not listed in the table result in illogical operation. The
DY/DT bits (bit 6 of the alarm day/date registers) con-
trol whether the alarm value stored in bits 0–5 of that
register reflects the day of the week or the date of the
month. If DY/DT is written to logic 0, the alarm is the
result of a match with date of the month. If DY/DT is
written to logic 1, the alarm is the result of a match
with day of the week. When the RTC register values
match alarm register settings, the corresponding alarm
flag A1F or A2F bit is set to logic 1. If the correspond-
ing alarm interrupt enable A1IE or A2IE bit is also set
to logic 1, the alarm condition activates the INT/SQW
signal if the INTCN bit is set to logic 1. The match is
tested on the once-per-second update of the time and
Table 3. Alarm Mask Bits
ALARM 1 REGISTER MASK BITS (BIT 7)
Alarm once a second
Alarm when seconds match
Alarm when minutes and seconds match
Alarm when hours, minutes, and seconds match
Alarm when date, hours, minutes, and seconds match
Alarm when day, hours, minutes, and seconds match
ALARM 2 REGISTER MASK BITS (BIT 7)
Alarm once per minute (00 seconds of every minute)
Alarm when minutes match
Alarm when hours and minutes match
Alarm when date, hours, and minutes match
Alarm when day, hours, and minutes match
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