DS1557 查看數據表（PDF） - Dallas Semiconductor -> Maxim Integrated

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DS1557

4MEG NV Y2KC Timekeeping RAM

Dallas Semiconductor -> Maxim Integrated 

ALARM MASK BITS Table 3

DS1557

AM4 AM3 AM2 AM1 ALARM RATE

1

1

1

1 Once per second

1

1

1

0 When seconds match

1

1

0

0 When minutes and seconds match

1

0

0

0 When hours, minutes, and seconds match

0

0

0

0 When date, hours, minutes, and seconds match

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 7FF0h) as shown in Figure 2 and 3. 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 tRC 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 back-up mode and power-up states.

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