Real Time Clock Multiplexed 242Byte 24-Pin SSOP T/R

The CMOS bq3285E/L is a low-power 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.

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 0.5µA 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 122us 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