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REV: 040805 
FEATURES 
Integrated NV SRAM, Real-Time Clock, 
Crystal, Power-Fail Control Circuit and 
Lithium Energy Source 
Clock Registers are Accessed Identically 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 
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
 Power Supply Tolerance 
DS1644 Only (DIP Module) 
Upward Compatible with the DS1643 
Timekeeping RAM to Achieve Higher 
RAM Density 
Standard JEDEC Bytewide 32k x 8 Static 
RAM Pinout 
DS1644P Only (PowerCap
 Module Board) 
Surface Mountable Package for Direct 
Connection to PowerCap Containing 
Battery and crystal 
Replaceable Battery (PowerCap) 
Power-Fail Output 
Pin-for-Pin Compatible with Other Densities 
of DS164XP Timekeeping RAM
Underwriters Laboratory (UL) Recognized 
ORDERING INFORMATION 
VOLTAGE 
RANGE (V) 
DS1644
0120+ 
5.0 
DS16440-120 
5.0 
DS1644P
120+ 
5.0 
DS1644P-120 
5.0 
*
DS9034-PCX, DS9034I-PCX, DS9034-PCX+ required (must be ordered separately).
A “+" indicates a lead-free product. The top mark will include a “+" symbol on lead-free devices. 
PIN CONFIGURATIONS 
PART 
TEMP RANGE PIN-PACKAGE 
TOP MARK 
0°C to +70°C 
0°C to +70°C 
0°C to +70°C 
0°C to +70°C 
32 EDIP (0.740a) 
32 EDIP (0.740a) 
34 PowerCap* 
34 PowerCap* 
DS1644+120 
DS1644-120 
DS1644P+120 
DS1644P-120 
1 
2 
3 
4 
5 
6 
7 
8 
9 
10 
11 
12 
13 
14 
15 
16 
17 
NC
NC
NC
PFO
V
CC
WE
OE
CE
DQ7
DQ6
DQ5
DQ4
DQ3
DQ2
DQ1
DQ0
GND
NC
A14
A13
A12
A11
A10
A9
A8
A7
A6
A5
A4
A3
A2
A1
A0
33
32
31
30
29
28
27
26
25
24
23
22
21
20
19
18
34
NC
X1 GND V
BAT
X2 
34-Pin PowerCap Module Board 
(Uses DS9034PCX PowerCap) 
15
13
27
26
25
24
23
22
21
20
19
18
17
28-Pin Encapsulated Package 
(720-mil Extended)
A7
A6
A5
A4
A3
A2
A1
A0
DQ0
DQ1
GND
DQ2
V
CC
WE
A13
A8
A9
A11
OE
A10
CE
DQ7
DQ6
DQ5
DQ4
DQ3
1
2
3
4
5
6
7
8
9
10
11
12
14
28
16
A12
A14
DS1644/DS1644P 
Nonvolatile Timekeeping RAM
www.maxim-ic.com 
PowerCap is a registered trademark of Dallas Semiconductor.