BQ3285EC Datasheet, PDF (6/26 Pages) Texas Instruments – Real-Time Clock (RTC)

bq3285EC/LC
32kHz Output
The bq3285EC/LC provides for a 32.768kHz output. For
the bq3285EC, the output is always active whenever VCC
is valid (VPFD + tCSR). The bq3285EC output is not af-
fected by the bit settings in Register A. Time-keeping
aspects, however, still require setting OS0-OS2. The
bq3285LC output is active when the oscillator is turned
on by setting the OSC0-OSC2 bits in Register A.
Interrupts
The bq3285EC/LC allows three individually selected in-
terrupt events to generate an interrupt request. These
three interrupt events are:
n The periodic interrupt, programmable to occur once
every 122µs to 500ms.
n The alarm interrupt, programmable to occur once per
second to once per day, is active in battery-backup
mode, providing a “wake-up” feature.
n The update-ended interrupt, which occurs at the end
of each update cycle.
Each of the three interrupt events is enabled by an indi-
vidual interrupt-enable bit in register B. When an event
occurs, its event flag bit in register C is set. If the corre-
sponding event enable bit is also set, then an interrupt
request is generated. The interrupt request flag bit
(INTF) of register C is set with every interrupt request.
Reading register C clears all flag bits, including INTF,
and makes INT high-impedance.
Two methods can be used to process bq3285EC/LC in-
terrupt events:
n Enable interrupt events and use the interrupt
request output to invoke an interrupt service routine.
n Do not enable the interrupts and use a polling
routine to periodically check the status of the flag
bits.
The individual interrupt sources are described in detail
in the following sections.
Table 3. Periodic Interrupt Rate
Register A Bits
OSC2
OSC1
OSC0
RS3
RS2
RS1
RS0
0
1
0
0
0
0
0
0
1
0
0
0
0
1
0
1
0
0
0
1
0
0
1
0
0
0
1
1
0
1
0
0
1
0
0
0
1
0
0
1
0
1
0
1
0
0
1
1
0
0
1
0
0
1
1
1
0
1
0
1
0
0
0
0
1
0
1
0
0
1
0
1
0
1
0
1
0
0
1
0
1
0
1
1
0
1
0
1
1
0
0
0
1
0
1
1
0
1
0
1
0
1
1
1
0
0
1
0
1
1
1
1
0
1
1
X
X
X
X
Periodic Interrupt
Period
Units
None
3.90625
ms
7.8125
ms
122.070
µs
244.141
µs
488.281
µs
976.5625
µs
1.95315
ms
3.90625
ms
7.8125
ms
15.625
ms
31.25
ms
62.5
ms
125
ms
250
ms
500
ms
same as above defined
by RS3–RS0
July 1996
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