Rainbow-electronics DS1558Y Instrukcja Użytkownika Pobierz pdf (Strona 9)

DS1558

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Table 3. ALARM MASK BITS

AM4 AM3 AM2 AM1 ALARM RATE

1111Once per second

1110When seconds match

1100When minutes and seconds match

1000When hours, minutes, and seconds match

0000When date, hours, minutes, and seconds match

When the RTC register values match alarm register settings, AF is set to a 1. If AE is also set to a 1, the

alarm condition activates the IRQ /FT pin. The IRQ /FT signal is cleared by a read or write to the flags

stable for as short as 15ns and either

OE or WE active, but is not guaranteed to be cleared unless t

fulfilled (Figure 2). Once the address has been selected for at least 15ns, the

IRQ /FT signal can be cleared

immediately, but is not guaranteed to be cleared until t

is fulfilled (Figure 3). The alarm flag is also

cleared by a read or write to the flags register, but the flag does not change states until the end of the

read/write cycle and the IRQ /FT signal has been cleared.

The IRQ /FT pin can also be activated in the battery-backed mode. The IRQ /FT goes low if an alarm

occurs and both ABE and AE are set. The ABE and AE bits are cleared during the power-up transition,

but an alarm generated during power-up sets 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 backup-battery mode and power-up states.

Figure 2. CLEARING IRQ WAVEFORMS ACTIVE

Figure 3. CLEARING IRQ WAVEFORMS

1 2 3 4 5 6 7 8 9 10 11 12 13 14 ... 17 18

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Rainbow-electronics DS1558Y Instrukcja Użytkownika Strona 9