BQ4852Y Datasheet, PDF (7/16 Pages) Texas Instruments – RTC Module With 512Kx8 NVSRAM

bq4852Y
read to the flags register. ALM3–ALM0 puts the alarm
into a periodic mode of operation. Table 5 describes the
selectable rates.
The alarm interrupt can be made active while the
bq4852Y is in the battery-backup mode by setting ABE
in the interrupts register. Normally, the INT pin tri-
states during battery backup. With ABE set, however, INT
is driven low if an alarm condition occurs and the AIE bit is
set. Because the AIE bit is reset during power-on reset, an
alarm generated during power-on reset updates only the
flags register. The user can read the flags register during
boot-up to determine if an alarm was generated during
power-on reset.
Power-Fail Interrupt
When VCC falls to the power-fail-detect point, the power-
fail flag PWRF is set. If the power-fail interrupt enable bit
(PWRIE) is also set, then INT is asserted low. The power-
fail interrupt occurs tWPT before the bq4852Y generates a
reset and deselects. The PWIE bit is cleared on power-up.
Battery-Low Warning
The bq4852Y checks the internal battery on power-up.
If the battery voltage is below 2.2V, the battery-low flag
BLF in the flags register is set to a 1 indicating that
clock and RAM data may be invalid.
Table 4. Periodic Rates
RS3
RS2
RS1
RS0
Interrupt Rate
0
0
0
0
None
0
0
0
1
10ms
0
0
1
0
100ms
0
0
1
1
122.07µ s
0
1
0
0
244.14µ s
0
1
0
1
488.281
0
1
1
0
976.5625
0
1
1
1
1.953125ms
1
0
0
0
3.90625ms
1
0
0
1
7.8125ms
1
0
1
0
15.625ms
1
0
1
1
31.25ms
1
1
0
0
62.5ms
1
1
0
1
125ms
1
1
1
0
250ms
1
1
1
1
500ms
ALM3
1
1
1
1
0
Table 5. Alarm Frequency (Alarm Bits DQ7 of Alarm Registers)
ALM2
1
1
1
0
0
ALM1
1
1
0
0
0
ALM0
1
0
0
0
0
Alarm Frequency
Once per second
Once per minute when seconds match
Once per hour when minutes, and seconds match
Once per day when hours, minutes, and seconds match
When date, hours, minutes, and seconds match
Aug. 1996
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