RTC Module With 114x8 NVSRAM And NVSRAM Control
The CMOS BQ4287 is Real-Time Clock Module With NVRAM Control 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 BQ4287 write-protects the Clock calendar, and storage Registers during power failure. The integral backup energy source then maintains data and operates the Clock and calendar.
The BQ4287 uses its integral battery-backup controller and battery to make a standard CMOS SRAM nonvolatile during power-fail conditions. During power-fail, the BQ4287 automatically write-protects the external SRAM and provides a VCC output sourced from its internal battery.
The BQ4287 is a fully compatible Real-Time Clock for IBM AT-compatible computers and other applications.
As shipped from Benchmarq, the backup cell is electrically isolated from the memory. Following the first application of VCC, this isolation is broken, and the backup cell provides data retention to the Clock internal RAM, VOUT, and CEOUT on subsequent power-downs.
The BQ4287 is functionally equivalent to the BQ4285 except that the battery (16, 20) and crystal pins (2, 3) are not accessible. These pins are connected internally to a coin cell and quartz crystal. The coin cell provides 130mAh of capacity. For a complete description of features, operating conditions, electrical characteristics, bus Timing and pin descriptions, see the BQ4285 data sheet.
By Texas Instruments
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