DS1340/DS1340C pdf datasheet (

The DS1340 is a real- time clock (RTC)/calendar that is
pin compatible and functionally equivalent to the ST
M41T00, including the software clock calibration. The
device additionally provides trickle-charge capability
on the VB ACKUP pin, a lower timekeeping voltage, and
an oscillat orSTOP flag. Block access of the register
map is identical to the ST device. Two additional registe rs,
which are accessed individually, are required for
the trickle charger and flag. The clock/calendar provides
seconds, minu tes, hours, day, date, month, and
year information. A built-in power-sense circuit detects
power failures and automat ically switches to the backup
supply. Reads and writes are inhibited while the
clock continues to run. The device is prog rammed serially
through an I2Cbidirectional bus.
Applications
Portable Instruments
Point-of-Sale Equipment
Medical Equipment
Telecommunications