DS1558

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BATTERY LONGIVITY

The battery lifetime is dependent on the RAM battery standby current and the DS1558 internal clock

50nA. The DS1558 has an internal circuit to prevent battery charging. No external protection components

are required, and none should be used. The DS1558 has two battery pins that operate independently; the

DS1558 selects the higher of the two inputs. If only one battery is used, the battery should be attached to

INTERNAL BATTERY MONITOR

The DS1558 constantly monitors the battery voltage of the internal battery. The battery-low flag (BLF)

bit of the flags register (B4 of 7FFF0h) is not writable and should always be a 0 when read. If a 1 is ever

present, both battery inputs are below 1.8V and both the contents of the RTC and RAM are questionable.

POWER-ON RESET

signal continues to be pulled low for a period of 40ms to 200ms. The power-on reset function is

independent of the RTC oscillator and thus is operational whether or not the oscillator is enabled.