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BQ4285Q- Datasheet(PDF) 1 Page - Texas Instruments |
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BQ4285Q- Datasheet(HTML) 1 Page - Texas Instruments |
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1 / 27 page  1 Features ® Direct clock/calendar replace- ment 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 0.5 µA load under bat- tery 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 in- terrupt 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 General Description The CMOS bq4285 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 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 dur- ing 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 com- puters 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 pro- vides a VCC output sourced from the clock backup battery. 28-Pin PLCC No longer available Pin Names AD0–AD7 Multiplexed address/data input/output MOT Bus type select input CS Chip select input AS Address strobe input DS Data strobe input R/W Read/write input INT Interrupt request output RST Reset input SQW Square wave output BC 3V backup cell input X1–X2 Crystal inputs NC No connect CEIN RAM chip enable input CEOUT RAM chip enable output VOUT Supply output VCC +5V supply VSS Ground SLUS002A JUNE 1991 - REVISED MAY 2004 1 PN428501.eps 24-Pin DIP or SOIC 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 BC INT RST DS VSS R/W AS CS VOUT X1 X2 AD0 AD1 AD2 AD3 AD4 AD5 AD6 AD7 VSS CEIN Pin Connections bq4285 Real-Time Clock (RTC) With NVRAM Control |
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