bq4285 Real-Time Clock (RTC) With NVRAM Control

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 compatible realtime 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 batterybackup controller to make a standard CMOS SRAM nonvolatile during power-fail conditions. During powerfail, the bq4285 automatically writeprotects 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 writeprotect control to external SRAM 

➤ 160 ns cycle time allows fast bus operation 

➤ Less than 0.5 µA 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 output 

➤ Three individually maskable interrupt event flags: - Periodic rates from 122 µs 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