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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 独立的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
注释：
87时钟格式 HH=小时，MM=分钟，SS=秒.
备用电池切换 备用电池转换功能是可自动在主电源和备用主电池、备用次电池或备用超级电容间转换的电路，转换电路是对主电源的监控实现的，所以和备 用电池的电压没有关系。
报警/中断 当时间和闹钟报警寄存器匹配时，激活中断输出，并对alarm flag置1﹣A/2﹣A分别表示该产品具有一组/两组报警寄存器。WD表示看门狗中断 输出
周期性中断 周期性中断功能（每秒、每分等等）。可用来指示时间和日期。AT8372、AT8565、AT8568、AT8390、AT9873、AT8563等芯片具有此功能
方波输出 输出和晶振相同频率的方波，芯景科技时钟芯片有如下几种方波输出：N沟开漏输出、CMOS推挽输出，32kHz方波可作为CPU的子时钟，或者作为 校准晶振频率精度的测试频率时钟
时钟校准 可通过CPU软件调整时间的快慢来补偿晶振频率。在一般的RTC中，可通过外部可调电容实现。在CPU中有温度信息的条件下，该功能也可用来作 为晶振温度补偿调整。
振荡器停止检测 停振检测电路可记录任何过去停振信息并记录在内部寄存器中，它可用来在重要时刻判断内部数据的有效性，例如上电时
涓流充电 当备用电源为可充电式纽扣锂电池或超级电容时，可使用主电源对其进行小电流充电。电流大小由充电支路（片内）上的二极管数目和充电电 阻大小决定。可通过特定寄存器对其进行设置。
用户RAM 在某些应用场合中，需要对数据或事件进行记录。因此，集成RAM的RTC产品可以解决关键数据的保存问题而无需外置存储结构。片内RAM通常为 SRAM、NVRAM，部分产品使用EEPROM
：郑 萍
：13602525829
Q：125952234
