DESCRIPTION
The DS1558 is a full function, year 2000-compliant (Y2KC), real-time clock/calendar with an RTC alarm, watchdog timer, power-on reset, battery monitor, and NV SRAM controller. User access to all registers within the DS1558 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 real-time clock (RTC), power-fail control circuit, and NV RAM controller
■ Clock registers are accessed identically to the static RAM; these registers are resident in the 16 top RAM locations
■ Century register
■ Greater than 10 years of timekeeping and data retention in the absence of power with small lithium coin cell(s) and low-leakage SRAM
■ 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
■ Underwriters Laboratory (UL) recognized