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DS1644L-120

Nonvolatile Timekeeping RAM

Dallas Semiconductor -> Maxim Integrated 

DS1644LPM

DS1644LPM

Nonvolatile Timekeeping RAM

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% VCC pow-

er supply tolerance

ORDERING INFORMATION

DS1644L–XXX Low Profile Module

–120 120 ns access

–150 150 ns access

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-

PIN ASSIGNMENT

NC

1

NC

2

NC

3

PFO

4

VCC

5

WE

6

OE

7

CE

8

DQ7

9

DQ6

10

DQ5

11

DQ4

12

DQ3

13

DQ2

14

DQ1

15

DQ0

16

GND

17

34

NC

33

NC

32

A14

31

A13

30

A12

29

A11

28

A10

27

A9

26

A8

25

A7

24

A6

23

A5

22

A4

21

A3

20

A2

19

A1

18

A0

34–PIN LOW PROFILE MODULE

PIN DESCRIPTION

A0–A14

– Address Input

CE

– Chip Enable

OE

– Output Enable

WE

– Write Enable

VCC

GND

– +5 Volts

– Ground

DQ0-DQ7

– Data Input/Output

NC

– No Connection

PFO

– Power Fail Output

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.

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.

041697 1/11

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