[UNITRODE]

General Description
The CMOS bq4285 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.

FEATUREs
➤ Direct clock/calendar replacement for IBM® AT-compatible computers and other applications
➤ Functionally compatible with the DS1285
   - Closely matches MC146818A pin configuration
➤ 114 bytes of general nonvolatile storage
➤ Automatic backup and writeprotect control to external SRAM
➤ 160 ns cycle time allows fast bus operation
➤ Selectable Intel or Motorola bus timing (PLCC), Intel bus timing (DIP and SOIC)
➤ Less than 0.5 µA load under battery operation
➤ 14 bytes for clock/calendar and control
➤ Calendar in day of the week, day of the month, months, and years, with automatic leap-year adjustment
➤ Time of day in seconds, minutes, and hours
   - 12- or 24-hour format
   - Optional daylight saving adjustment
➤ BCD or binary format for clock and calendar data
➤ Programmable square wave output
➤ Three individually maskable interrupt event flags:
   - Periodic rates from 122 µs to 500 ms
   - Time-of-day alarm once per second to once per day
   - End-of-clock update cycle
➤ 24-pin plastic DIP or SOIC