The CMOS bq3287/bq3287A 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 114 bytes of general nonvolatile storage. The bq3287A version is identical to the bq3287, with the addition of the RAM clear input.
●The bq3287 is a fully compatible real-time clock for IBM AT-compatible computers and other applications. The bq3287 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 from Benchmarq, the real time clock is turned off to maximize battery capacity for in-system operation.
●The bq3287 is functionally equivalent to the bq3285, except that the battery (16, 20) and crystal (2, 3) pins 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 bq3285 data sheet.
● Direct clock/calendar replacement for IBM\xAE AT-compatible computers and other applications
● Functionally compatible with the DS1287/DS1287A and MC146818A
● 114 bytes of general nonvolatile storage
● Integral lithium cell and crystal
● 160 ns cycle time allows fast bus operation
● Selectable Intel or Motorola bus timing
● 14 bytes for clock/calendar and control
● BCD or binary format for clock and calendar data
● 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
