General Description

    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.

Applications

• Embedded Systems
• Utility Meters
• Security Systems
• Network Hubs, Bridges, and Routers

Features

• Drop-In Replacement for IBM AT Computer Clock/Calendar
• RTC Counts Seconds, Minutes, Hours, Day, Date, Month, and Year with Leap Year CompensationThrough 2099
• Binary or BCD Time Representation
• 12-Hour or 24-Hour Clock with AM and PM in 12-Hour Mode
• Daylight Saving Time Option
• Selectable Intel or Motorola Bus Timing
• Interfaced with Software as 128 RAM Locations 
• 14 Bytes of Clock and Control Registers
• 114 Bytes of General-Purpose, Battery-Backed RAM (113 Bytes in the AT12887)
• RAM Clear Function (AT12885, AT12887)
• Interrupt Output with Three Independently Maskable Interrupt Flags
• Time-of-Day Alarm Once Per Second to Once Per Day
• Periodic Rates from 122μs to 500ms
• End-of-Clock Update Cycle Flag
• Programmable Square-Wave Output
• Automatic Power-Fail Detect and Switch Circuitry
• Optional 28-Pin PLCC Surface Mount Package or32-Pin TQFP (AT12885)
• Optional Encapsulated DIP (EDIP) Package with Integrated Crystal and Battery (AT12887, AT12887)
• Optional Industrial Temperature Range Available
• Underwriters Laboratory (UL) Recognized
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