General Description
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 VBACKUP pin, a lower timekeeping voltage, and an oscillator STOP flag. Block access of the register map is identical to the ST device. Two additional registers, which are accessed individually, are required for the trickle charger and flag. The clock/calendar provides seconds, minutes, hours, day, date, month, and year information. A built-in power-sense circuit detects power failures and automatically switches to the backup supply. Reads and writes are inhibited while the clock continues to run. The device is programmed serially through an I2C bidirectional bus.

Features
♦ Enhanced Second Source for the ST M41T00
♦ Available in a Surface-Mount Package with an
   Integrated Crystal (DS1340C)
♦ Fast (400kHz) I2C Interface
♦ Software Clock Calibration
♦ RTC Counts Seconds, Minutes, Hours, Day, Date,
   Month, and Year
♦ Automatic Power-Fail Detect and Switch Circuitry
♦ Trickle-Charge Capability
♦ Low Timekeeping Voltage Down to 1.3V
♦ Three Operating Voltage Ranges (1.8V, 3V, and 3.3V)
♦ Oscillator Stop Flag
♦ Available in 8-Pin µSOP or SO Packages
♦ Underwriters Laboratories (UL) Recognized

Applications
   Portable Instruments
   Point-of-Sale Equipment
   Medical Equipment
   Telecommunications