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
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