Features
Direct clock/calendar replacement
for IBM® AT-compatible
computers and other applications
Functionally compatible with the
DS1285
- Closely matches MC146818A
pin configuration
2.7–3.6V operation (bq3285L);
4.5–5.5V operation (bq3285E)
242 bytes of general nonvolatile
storage
32.768kHz output for power management
System wake-up capability—
alarm interrupt output active in
battery-backup mode
Less than 0.5mA load under battery
operation
Selectable Intel or Motorola bus
timing
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, SOIC, or
SSOP

General Description
The CMOS bq3285E/L is a lowpower
microprocessor peripheral
providing a time-of-day clock and
100-year calendar with alarm features
and battery operation. The
bq3285L supports 3V systems.
Other bq3285E/L 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 bq3285E/L write-protects the
clock, calendar, and storage registers
during power failure. A backup
battery then maintains data and operates
the clock and calendar.
The bq3285E/L 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.