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