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bq4285 - Real-Time Clock (RTC) With NVRAM Control (Rev. A)
Texas Instruments
Description
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.
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 Automatic backup and write-protect control to external SRAM 160 ns cycle time allows fast bus operation Less than 0.5µA load under battery operation 14 bytes for clock/calendar and control 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 BCD or binary format for clock and calendar data Programmable square wave out-put Three individually maskable interrupt event flags: Periodic rates from 122 us to 500 ms Time-of-day alarm once per second to once per day End-of-clock update cycle 24-pin plastic DIP or SOIC
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