DS1554 Maxim, DS1554 Datasheet - Page 6

• Manufacturer Part Number: DS1554
• Description: The DS1554 is a full-function, year 2000-compliant (Y2KC), real-time clock/calendar (RTC) with an RTC alarm, watchdog timer, power-on reset, battery monitor, and 32k x 8 nonvolatile static RAM
• Manufacturer: Maxim

DS1554 256k, Nonvolatile, Y2K-Compliant Timekeeping RAM
BATTERY LONGEVITY
The DS1554 has a lithium power source that is designed to provide energy for the clock activity, and
clock and RAM data retention when the V
supply is not present. The capability of this internal power
CC
supply is sufficient to power the DS1554 continuously for the life of the equipment in which it is
installed. For specification purposes, the life expectancy is 10 years at 25C with the internal clock
oscillator running in the absence of V
. Each DS1554 is shipped from Maxim with its lithium energy
CC
source disconnected, guaranteeing full energy capacity. When V
is first applied at a level greater than
CC
V
, the lithium energy source is enabled for battery backup operation. Actual life expectancy of the
PF
DS1554 will be much longer than 10 years since no internal battery energy is consumed when V
is
CC
present.
INTERNAL BATTERY MONITOR
The DS1554 constantly monitors the battery voltage of the internal batter. The Battery Low Flag (BLF)
bit of the Flags Register (B4 of 7FFF0h) is not writeable and should always be a 0 when read. If a 1 is
ever present, an exhausted lithium energy source is indicated and both the contents of the RTC and RAM
are questionable.
POWER-ON RESET
A temperature compensated comparator circuit monitors the level of V
. When V
falls to the power-
CC
CC
fail trip point, the RST signal (open drain) is pulled low. When V
returns to nominal levels, the RST
CC
signal continues to be pulled low for a period of 40 ms to 200 ms. The power-on reset function is
independent of the RTC oscillator and thus is operational whether or not the oscillator is enabled.
CLOCK OPERATIONS
Table 2 and the following paragraphs describe the operation of RTC, alarm, and watchdog functions.
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