Rainbow-electronics DS1543 Instrukcja Użytkownika Pobierz pdf (Strona 7)

DS1543

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When the RTC register values match alarm register settings, the Alarm Flag bit (AF) is set to a 1. If

Alarm Flag Enable (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 register (Address 1FF0h) as shown in Figure 2. The

IRQ /FT signal may be cleared by having the address stable for as short as 15 ns and either CE or WE

active, but is not guaranteed to be cleared unless t

is fulfilled. The alarm flag is also cleared by a read

or write to the Flags register, but the flag will not change states until the end of the read/write cycle and

the IRQ /FT signal has been cleared.

CLEARING IRQ WAVEFORMS Figure 2

CLEARING IRQ WAVEFORMS Figure 3

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.

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Rainbow-electronics DS1543 Instrukcja Użytkownika Strona 7