The CMOS bq3287E/bq3287EA is a low-power microprocessor peripheral providing a time-of-day clock and 100-year calendar with alarm features and battery operation. Other features include three maskable interrupt sources, square-wave output, and 242 bytes of general nonvolatile storage. A 32.768kHz output is available for sustaining power-management activities. Wake-up capability is provided by an alarm interrupt, which is active in battery-backup mode. The bq3287EA version is identical to the bq3287E, with the addition of the RAM clear input.
●The bq3287E is a fully compatible real-time clock for IBM AT-compatible computers and other applications. The bq3287E write-protects the clock, calendar, and storage registers during power failure. The integral backup energy source then maintains data and operates the clock and calendar.
●As shipped, the real time clock is turned off to maximize battery capacity for in-system operation.
●The bq3287E is functionally equivalent to the bq3285E, except the battery (16,20) and crystal pins (2,3) are not accessible. These pins are connected internally to a coin cell and quartz crystal. The coin cell is sized to provide 10 years of data retention and clock operation in the absence of power. For a complete description of features, operating conditions, electrical characteristics, bus timing, and pin descriptions, see the bq3285E data sheet.
● Direct clock/calendar replacement for IBM\xAE AT-compatible computers and other applications
● Functionally compatible with the DS1287/DS1287A and MC146818A/ MC146818B
● 242 bytes of general nonvolatile storage
● Provides a 32.768kHz output for power management
● System wake-up capability-alarm interrupt active in battery-backup mode
● Integral lithium cell and crystal
● 160 ns cycle time allows fast bus operation
● 14 bytes for clock/calendar and control
● Time of day in seconds, minutes, and hours
● 12- or 24-hour format
● Optional daylight saving adjustment
● Calendar in day of the week, day of the month, months, and years with automatic leap year adjustment
● Programmable square wave output
● Three individually maskable interrupt event flags:
● Periodic rates from 122us to 500ms
● Time-of-day alarm once per second to once per day
● End-of-clock update cycle
● Better than one minute per month clock accuracy
