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
160ns cycle time allows fast bus
operation
Selectable Intel or Motorola bus
timing
Less than 0.5mA load under battery
operation
14 bytes for clock/calendar and
control
BCD or binary format for clock
and calendar data
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
Programmable square wave output
Three individually maskable interrupt
event flags:
- Periodic rates from 122ms to
500ms
- Time-of-day alarm once per
second to once per day
- End-of-clock update cycle
24-pin plastic DIP or SOIC

General Description
The CMOS bq3285 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 bq3285 write-protects the clock,
calendar, and storage registers during
power failure. A backup battery
then maintains data and operates the
clock and calendar.
The bq3285 is a fully compatible
real-time clock for IBM AT compatible
computers and other applications.
The only external components
are a 32.768kHz crystal and
a backup battery