DESCRIPTION
The DS1556 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 128k x 8 nonvolatile static RAM. User access to all registers within the DS1556 is accomplished with a byte-wide interface as shown in Figure 1. The RTC registers contain century, year, month, date, day, hours, minutes, and seconds data in 24-hour BCD format. Corrections for day of month and leap year are made automatically.

FEATURES
■ Integrated NV SRAM, Real-Time Clock (RTC), Crystal, Power-Fail Control Circuit, and Lithium Energy Source
■ Clock Registers are Accessed Identically to the Static RAM; These Registers Reside in the 16 Top RAM Locations
■ Century Byte Register (i.e., Y2K Compliant)
■ Totally Nonvolatile with Over 10 Years of Operation in the Absence of Power
■ Precision Power-On Reset
■ Programmable Watchdog Timer and RTC Alarm
■ BCD-Coded Year, Month, Date, Day, Hours, Minutes, and seconds with Automatic LeapYear Compensation Valid Up to the Year 2100
■ Battery Voltage-Level Indicator Flag
■ Power-Fail Write Protection Allows for
10% VCC Power-Supply Tolerance
■ Lithium Energy Source is Electrically Disconnected to Retain Freshness Until Power is Applied for the First Time
■ Also Available in Industrial Temperature Range: -40°C to +85°C