BQ4285

具有 114x8 NVSRAM 和 NVSRAM 控制的 RTC IC

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.

The bq4285 write-protects the clock, calendar, and storage registers during power failure. A backup battery then maintains data and operates the clock and calendar.

The bq4285 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.

The bq4285 integrates a battery-backup controller to make a standard CMOS SRAM nonvolatile during power-fail conditions. During power-fail, the bq4285 automatically write-protects the external SRAM and provides a VCC output sourced from the clock backup battery.

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Direct clock/calendar replacement for IBM® AT-compatible computers and other applications

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Functionally compatible with the DS1285

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Closely matches MC146818A pin configuration

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114 bytes of general nonvolatile storage

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Automatic backup and write-protect control to external SRAM

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160 ns cycle time allows fast bus operation

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Less than 0.5µA load under battery operation

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14 bytes for clock/calendar and control

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Calendar in day of the week, day of the month, months, and years, with automatic leap-year adjustment

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Time of day in seconds, minutes, and hours

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12- or 24-hour format

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Optional daylight saving adjustment

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BCD or binary format for clock and calendar data

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Programmable square wave out-put

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Three individually maskable interrupt event flags:

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Periodic rates from 122 us to 500 ms

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Time-of-day alarm once per second to once per day

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End-of-clock update cycle

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24-pin plastic DIP or SOIC