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PDF DS1644LPM Data sheet ( Hoja de datos )

Número de pieza DS1644LPM
Descripción Nonvolatile Timekeeping RAM
Fabricantes Dallas Semiconducotr 
Logotipo Dallas Semiconducotr Logotipo



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No Preview Available ! DS1644LPM Hoja de datos, Descripción, Manual

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
NC
NC
PFO
VCC
WE
OE
CE
DQ7
DQ6
DQ5
DQ4
DQ3
DQ2
DQ1
DQ0
GND
1 34
2 33
3 32
4 31
5 30
6 29
7 28
8 27
9 26
10 25
11 24
12 23
13 22
14 21
15 20
16 19
17 18
34–PIN LOW PROFILE MODULE
NC
NC
A14
A13
A12
A11
A10
A9
A8
A7
A6
A5
A4
A3
A2
A1
A0
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

1 page




DS1644LPM pdf
DS1644LPM
DATA RETENTION MODE
When VCC is within nominal limits (VCC > 4.5 volts) the
DS1644L can be accessed as described above with
read or write cycles. However, when VCC is below the
power fail point VPF (point at which write protection oc-
curs) the internal clock registers and RAM are blocked
from access. This is accomplished internally by inhibit-
ing access via the CE signal. At this time the power–fail
output signal (PFO) will be driven active low and will
remain active until VCC returns to nominal levels. When
VCC falls below the level of the internal battery supply,
power input is switched from the VCC pin to the internal
battery and clock activity, RAM, and clock data are
maintained from the battery until VCC is returned to
nominal level.
INTERNAL BATTERY LONGEVITY
The DS1644L has a self contained lithium power source
that is designed to provide energy for clock activity, and
clock and RAM data retention when the VCC supply is
not present. The capability of this internal power supply
is sufficient to power the DS1644L continuously for the
life of the equipment in which it is installed. For specifi-
cation purposes, the life expectancy is 10 years at 25°C
with the internal clock oscillator running in the absence
of VCC power. The DS1644L is shipped from Dallas
Semiconductor with the clock oscillator turned off, so
the expected life should be considered to start from the
time the clock oscillator is first turned on. Actual life ex-
pectancy of the DS1644L will be much longer than 10
years since no internal lithium battery energy is con-
sumed when VCC is present. In fact, in most applica-
tions, the life expectancy of the DS1644L will be approx-
imately equal to the shelf life (expected useful life of the
lithium battery with no load attached) of the lithium bat-
tery which may prove to be as long as 20 years.
041697 5/11

5 Page





DS1644LPM arduino
DS1644LPM 34–PIN LOW PROFILE MODULE
E
B
A
F
D
C
NOTE:
Please contact the factory for information on PLCC Sur-
face mountable sockets.
DS1644LPM
PKG
DIM
A
B
C
D
E
F
INCHES
MIN
0.955
0.840
0.230
0.975
0.047
0.015
MAX
0.980
0.855
0.250
0.995
0.053
0.025
041697 11/11

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