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BQ4287 Datasheet(PDF) 1 Page - Texas Instruments |
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BQ4287 Datasheet(HTML) 1 Page - Texas Instruments |
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1 / 8 page  Features ® Direct clock/calendar replace- ment for IBM® AT-compatible computers and other applications ® Functionally compatible with the DS1287/DS1287A and MC146818A ® 114 bytes of general nonvolatile storage ® Automatic backup supply and write-protection to make external SRAM nonvolatile ® Integral lithium cell and crystal ® 160 ns cycle time allows fast bus operation ® Intel 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 out- put ® Three individually maskable in- terrupt event flags: - Periodic rates from 122 µsto 500 ms - Time-of-day alarm once per second to once per day - End-of-clock update cycle ® Better than one minute per month clock accuracy General Description The CMOS bq4287 is a low-power microprocessor peripheral providing a time-of-day clock and 100-year cal- endar with alarm features and bat- tery operation. Other features in- clude three maskable interrupt sources, square wave output, and 114 bytes of general nonvolatile storage. The bq4287 write-protects the clock, calendar, and storage registers dur- ing power failure. The integral backup energy source then main- tains 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 subse- quent power-downs. The bq4287 is functionally equiva- lent 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 pro- vides 130mAh of capacity. For a complete description of features, op- erating conditions, electrical charac- teristics, bus timing, and pin de- scriptions, see the bq4285 data sheet. 1 Pin Names AD0–AD7 Multiplexed address/data input/output CS Chip select input ALE Address strobe input RD Data strobe input WR Read/write input INT Interrupt request output RST Reset input SQW Square wave output CEIN RAM chip enable input CEOUT RAM chip enable output NC No connect VOUT Supply output VCC +5V supply VSS Ground 1 PN428701.eps 24-Pin DIP Module 2 3 4 5 6 7 8 24 23 22 21 20 19 18 17 9 10 16 15 11 12 14 13 VCC SQW CEOUT NC INT RST RD NC WR ALE CS VOUT NC NC AD0 AD1 AD2 AD3 AD4 AD5 AD6 AD7 VSS CEIN bq4287 Pin Connections Real-Time Clock Module With NVRAM Control Caution: Take care to avoid inadvertent dis- charge through VOUT and CEOUT after battery isolation has been broken. Nov. 1993 C |
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