DESCRIPTION
The DS1557 is a full function, year 2000-compliant (Y2KC), real-time clock/calendar (RTC) with a RTC alarm, watchdog timer, power-on reset, battery monitor, and 512k x 8 non-volatile static RAM. User access to all registers within the DS1557 is accomplished with a bytewide 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, crystal, power-fail control circuit and lithium energy source
◾ Clock registers are accessed identically to the static RAM; these registers are resident in the 16 top RAM locations
◾ Century byte register; i.e., Y2K complaint
◾ 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 leap year 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