
DS1557 4Meg, Nonvolatile, Y2K-Compliant Timekeeping RAM
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Figure 3. Clearing
IRQ Waveforms
The
IRQ/FT pin can also be activated in the battery-backed mode. The IRQ/FT will go low if an alarm
occurs and both ABE and AE are set. The ABE and AE bits are cleared during the power-up transition,
however an alarm generated during power-up will set AF. Therefore, the AF bit can be read after system
power-up to determine if an alarm was generated during the power-up sequence. Figure 4 illustrates
alarm timing during the battery-backup mode and power-up states.
Figure 4. Backup Mode Alarm Waveforms
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18
8
CE =0
7FFF0h