The AT12885, AT12887 real-time clocks (RTCs) devices provide a real-time clock/calendar, one time-of-day alarm, three maskable interrupts with a common interrupt output, a programmable square wave, and 114 bytes of battery-backed static RAM.The AT12887 integrates a quartz crystal and lithium energy source into a 24-pin encapsulated DIP package. The AT12887 adds a century byte at address 32h. For all devices, the date at the end of the month is automatically adjusted for months with fewer than 31 days, including correction for leap years. The devices also operate in either 24-hour or 12-hour format with an AM/PM indicator. A precision temperature-compensated circuit monitors the status of VCC. If a primary power failure is detected, the device automatically switches to a backup supply. A lithium coin-cell battery can be connected to the VBAT input pin on the AT12885 to maintain time and date operation when primary power is absent. The device is accessed through a multiplexed byte-wide interface, which sup-ports both Intel and Motorola modes.