DS1557

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The RTC Registers are double-buffered into an internal and external set. The user has direct access to the

external set. Clock/calendar updates to the external set of registers can be disabled and enabled to allow

the user to access static data. Assuming the internal oscillator is turned on, the internal set of registers are

continuously updated; this occurs regardless of external registers settings to guarantee that accurate RTC

information is always maintained.

match user programmed alarm values. The interrupt is always available while the device is powered from

the system supply and can be programmed to occur when in the battery backed state to serve as a system

monitored and an interrupt or reset output will be activated if the correct activity is not detected within

programmed limits. The DS1557 power-on reset can be used to detect a system power down or failure

for this function.

The DS1557 also contains its own power-fail circuitry which automatically deselects the device when the

DS1557 BLOCK DIAGRAM Figure 1