BQ4822Y Datasheet, PDF (7/16 Pages) Texas Instruments – RTC Module With 8Kx8 NVSRAM

bq4822Y
Table 4. Periodic Rates
Interrupt
RS3
RS2
RS1
RS0
Rate
Table 5. Alarm Frequency
(Alarm Bits DQ7 of Alarm Registers)
ALM3 ALM2 ALM1 ALM0 Alarm Frequency
0
0
0
0
None
0
0
0
1
10ms
1
1
1
1 Once per second
1
1
1
0 Once per minute
when seconds match
0
0
1
0
100ms
1
1
0
0 Once per hour when
minutes, and seconds
0
0
1
1
122.07µ s
match
1
0
0
0 Once per day when
0
1
0
0
244.14µ s
hours, minutes, and
seconds match
0
1
0
1
488.281µ s
0
0
0
0 When date, hours,
0
1
1
0
976.5625
minutes, and seconds
match
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
Alarm Interrupt
Registers 1FF5–1FF2 program the real-time clock
alarm. During each update cycle, the bq4822Y compares
the date, hours, minutes, and seconds in the clock regis-
ters with the corresponding alarm registers. If a match
between all the corresponding bytes is found, the alarm
flag AF in the flags register is set. If the alarm inter-
rupt is enabled with AIE, an interrupt request is gener-
ated on INT. The alarm condition is cleared by a read to
the flags register. ALM3–ALM0 puts the alarm into a
periodic mode of operation. Table 5 describes the se-
lectable rates.
The alarm interrupt can be made active while the
bq4822Y 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 re-
set 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 bq4822Y
generates a reset and deselects. The PWRIE bit is
cleared on power-up.
Battery-Low Warning
The bq4822Y 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.
May 1997
7