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BQ3285S-SB2TR Datasheet(PDF) 6 Page - Texas Instruments |
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BQ3285S-SB2TR Datasheet(HTML) 6 Page - Texas Instruments |
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6 / 26 page  Square-Wave Output The bq3285 divides the 32.768kHz oscillator frequency to produce the 1Hz update frequency for the clock and calendar. Thirteen taps from the frequency divider are fed to a 16:1 multiplexer circuit. The output of this mux is fed to the SQW output and periodic interrupt genera- tion circuitry. The four least-significant bits of register A, RS0–RS3, select among the 13 taps (see Table 3). The square-wave output is enabled by writinga1tothe square-wave enable bit (SQWE) in register B. Interrupts The bq3285 allows three individually selected interrupt events to generate an interrupt request. These three in- terrupt events are: n The periodic interrupt, programmable to occur once every 122 µs to 500ms n The alarm interrupt, programmable to occur once per second to once per day 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 bq3285 interrupt 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. 6 Register A Bits Square Wave Periodic Interrupt RS3 RS2 RS1 RS0 Frequency Units Period Units 0000 None None 0001 256 Hz 3.90625 ms 0010 128 Hz 7.8125 ms 0011 8.192 kHz 122.070 µs 0100 4.096 kHz 244.141 µs 0101 2.048 kHz 488.281 µs 0110 1.024 kHz 976.5625 µs 0111 512 Hz 1.95315 ms 1000 256 Hz 3.90625 ms 1001 128 Hz 7.8125 ms 1010 64 Hz 15.625 ms 1011 32 Hz 31.25 ms 1100 16 Hz 62.5 ms 1101 8 Hz 125 ms 1110 4 Hz 250 ms 1111 2 Hz 500 ms Table 3. Square-Wave Frequency/Periodic Interrupt Rate bq3285 |
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