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:
