DS1543-XXX Maxim Integrated Products, DS1543-XXX Datasheet - Page 7

• Manufacturer Part Number: DS1543-XXX
• Description: 64K NV Real Time Clocks RAM
• Manufacturer: Maxim Integrated Products

DS1543
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
/FT pin. The
/FT
IRQ
IRQ
signal is cleared by a read or write to the Flags register (Address 1FF0h) as shown in Figure 2. The
/FT signal may be cleared by having the address stable for as short as 15 ns and either
or
IRQ
CE
WE
active, but is not guaranteed to be cleared unless t
is fulfilled. The alarm flag is also cleared by a read
RC
or write to the Flags register, but the flag will not change states until the end of the read/write cycle and
the
/FT signal has been cleared.
IRQ
CLEARING IRQ WAVEFORMS Figure 2
CLEARING IRQ WAVEFORMS Figure 3
The
/FT pin can also be activated in the battery-backed mode. The
/FT will go low if an alarm
IRQ
IRQ
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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