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DS1644LPM Datasheet(PDF) 1 Page - Dallas Semiconductor |
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DS1644LPM Datasheet(HTML) 1 Page - Dallas Semiconductor |
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1 / 11 page  ECopyright 1995 by Dallas Semiconductor Corporation. All Rights Reserved. For important information regarding patents and other intellectual property rights, please refer to Dallas Semiconductor data books. DS1644LPM Nonvolatile Timekeeping RAM DS1644LPM 041697 1/11 FEATURES • Upward compatible with the DS1643AL Timekeeping RAM to achieve higher RAM density • Integrated NV SRAM, real time clock, crystal, power– fail control circuit and lithium energy source • Low profile socketable module – 255 mil package height • Clock registers are accessed identical to the static RAM. These registers are resident in the eight top RAM locations. • Totally nonvolatile with over 10 years of operation in the absence of power • Access time of 120 ns and 150 ns • Quartz accuracy ±1 minute a month @ 25°C, factory calibrated • BCD coded year, month, date, day, hours, minutes, and seconds with leap year compensation valid up to 2100 • Power–fail write protection allows for ±10% V CC pow- er supply tolerance ORDERING INFORMATION DS1644L–XXX –120 120 ns access 150 ns access –150 Low Profile Module PIN ASSIGNMENT OE CE WE PFO VCC 1 2 3 4 5 6 7 8 9 10 11 12 13 34 33 32 31 30 29 28 27 26 25 24 23 22 14 15 16 17 21 20 19 18 NC NC A14 A13 A12 A11 A10 A9 A8 A7 A6 A5 A4 A3 A2 A1 A0 NC NC NC DQ7 DQ6 DQ5 DQ4 DQ3 DQ2 DQ1 DQ0 GND 34–PIN LOW PROFILE MODULE PIN DESCRIPTION A0–A14 – Address Input CE – Chip Enable OE – Output Enable WE – Write Enable VCC – +5 Volts GND – Ground DQ0-DQ7 – Data Input/Output NC – No Connection PFO – Power Fail Output DESCRIPTION The DS1644L is a low profile module that requires a PLCC surface mountable socket and is functionally equivalent to the DS1644. The DS1644L is a 32K x 8 nonvolatile static RAM with a full function real time clock which are both accessible in a Byte–wide format. The real time clock information resides in the eight upper- most RAM locations. The RTC registers contain year, month, date, day, hours, minutes, and seconds data in 24 hour BCD format. Corrections for the day of the month and leap year are made automatically. The RTC clock registers are double buffered to avoid access of in- correct data that can occur during clock update cycles. The double buffered system also prevents time loss as the timekeeping countdown continues unabated by ac- cess to time register data. The DS1644L also contains its own power–fail circuitry which deselects the device when the VCC supply is in an out–of–tolerance condi- tion. This feature prevents loss of data from unpredict- able system operation brought on by low VCC as errant access and update cycles are avoided. |
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