The DS1743 is a full-function, year-2000-compliant (Y2KC), real-time clock/calendar (RTC) and 8k x 8 nonvolatile static RAM. User access to all registers within the DS1743 is accomplished with a bytewide interface as shown in Figure 1 in the full data sheet. The RTC information and control bits reside in the eight uppermost RAM locations. The RTC registers contain century, year, month, date, day, hours, minutes, and seconds data in 24-hour binary-coded decimal (BCD) format. Corrections for the day of the month and leap year are made automatically. The RTC clock registers are double buffered to avoid access of incorrect data that can occur during clock update cycles. The double-buffered system also prevents time loss as the timekeeping countdown continues unabated by access to time register data. The DS1743 also contains its own power-fail circuitry, which deselects the device when the V_CC supply is in an out-of-tolerance condition. When V_CC is above V_PF, the device is fully accessible. When V_CC is below V_PF, the internal active-low CE signal is forced high, preventing any access. When V_CC rises above V_PF, access remains inhibited for T_REC, allowing time for the system to stabilize. These features prevent loss of data from unpredictable system operation brought on by low V_CC as errant access and update cycles are avoided.