19-5500; Rev 9/10
DS1556
1M, Nonvolatile, Y2K-Compliant
Timekeeping RAM
www.maxim-ic.com
FEATURES
Integrated NV SRAM, Real-Time Clock
(RTC), Crystal, Power-Fail Control Circuit,
and Lithium Energy Source
TOP VIEW
RST
A16
A14
A12
A7
A6
A5
A4
A3
A2
A1
Clock Registers are Accessed Identically to
the Static RAM; These Registers Reside in
the 16 Top RAM Locations
Century Byte Register (i.e., Y2K Compliant)
Totally Nonvolatile with Over 10 Years of
Operation in the Absence of Power
Precision Power-On Reset
Programmable Watchdog Timer and RTC
Alarm
PIN CONFIGURATIONS
Battery Voltage-Level Indicator Flag
Power-Fail Write Protection Allows for 10%
VCC Power-Supply Tolerance
Also Available in Industrial Temperature
Range: -40°C to +85°C
VCC
A15
DQ0
13
20
DQ6
DQ1
DQ2
14
19
DQ5
15
18
DQ4
GND
16
17
DQ3
IRQ/FT
WE
A13
A8
A9
A11
OE
A10
CE
DQ7
Encapsulated DIP
Lithium Energy Source is Electrically
Disconnected to Retain Freshness Until
Power is Applied for the First Time
32
31
30
29
28
27
26
25
24
23
22
21
A0
BCD-Coded Year, Month, Date, Day, Hours,
Minutes, and seconds with Automatic LeapYear Compensation Valid Up to the Year
2100
1
Maxim
2 DS1556
3
4
5
6
7
8
9
10
11
12
IRQ/FT
A15
A16
RST
VCC
WE
OE
CE
DQ7
DQ6
DQ5
DQ4
DQ3
DQ2
DQ1
DQ0
GND
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
Maxim
DS1556
X1
GND
VBAT
X2
34
33
32
31
30
29
28
27
26
25
24
23
22
21
20
19
18
N.C.
N.C.
A14
A13
A12
A11
A10
A9
A8
A7
A6
A5
A4
A3
A2
A1
A0
PowerCap Module Board
(Uses DS9034PCX PowerCap)
Note: Some revisions of this device may incorporate deviations from published specifications known as errata. Multiple revisions of any device
may be simultaneously available through various sales channels. For information about device errata, click here: www.maxim-ic.com/errata.
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DS1556 1M, Nonvolatile, Y2K-Compliant Timekeeping RAM
PIN DESCRIPTION
A0–A16
DQ0–DQ7
IRQ/FT
RST
CE
OE
WE
VCC
GND
N.C.
X1, X2
VBAT
- Address Input
- Data Input/Outputs
- Interrupt, Frequency Test Output (Open Drain)
- Power-On Reset Output (Open Drain)
- Chip Enable
- Output Enable
- Write Enable
- Power Supply Input
- Ground
- No Connection
- Crystal Connection
- Battery Connection
ORDERING INFORMATION
PART
TEMP RANGE
VOLTAGE
(V)
PIN-PACKAGE
TOP MARK**
DS1556-70+
DS1556-70IND+
DS1556P-70+
DS1556P-70IND+
DS1556W-120+
DS1556W-120IND+
DS1556WP-120+
DS1556WP-120IND+
0°C to +70°C
-40°C to +85°C
0°C to +70°C
-40°C to +85°C
0°C to +70°C
-40°C to +85°C
0°C to +70°C
-40°C to +85°C
5.0
5.0
5.0
5.0
3.3
3.3
3.3
3.3
32 EDIP (0.740a)
32 EDIP (0.740a)
34 PowerCap*
34 PowerCap*
32 EDIP (0.740a)
32 EDIP (0.740a)
34 PowerCap*
34 PowerCap*
DS1556+070
DS1556+070 IND
DS1556P+70
DS1556P+70 IND
DS1556W+120
DS1556W+120 IND
DS1556WP+120
DS1556WP+120 IND
+Denotes a lead(Pb)-free/RoHS-compliant package.
*DS9034-PCX+ or DS9034I-PCX+ required (must be ordered separately).
**A “+” in top mark denotes a lead(Pb)-free device. An “IND” anywhere on the top mark indicates an industrial temperature grade device.
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DS1556 1M, Nonvolatile, Y2K-Compliant Timekeeping RAM
DESCRIPTION
The DS1556 is a full-function, year-2000-compliant (Y2KC), real-time clock/calendar (RTC) with an
RTC alarm, watchdog timer, power-on reset, battery monitor, and 128k x 8 nonvolatile static RAM. User
access to all registers within the DS1556 is accomplished with a byte-wide interface as shown in Figure 1.
The RTC registers contain century, year, month, date, day, hours, minutes, and seconds data in 24-hour
BCD format. Corrections for day of month and leap year are made automatically.
The RTC registers are double-buffered into an internal and external set. The user has direct access to the
external set. Clock/calendar updates to the external set of registers can be disabled and enabled to allow
the user to access static data. Assuming the internal oscillator is turned on, the internal set of registers is
continuously updated, which occurs regardless of external registers settings to guarantee that accurate
RTC information is always maintained.
The DS1556 has interrupt (IRQ/FT) and reset (RST) outputs which can be used to control CPU activity.
The IRQ/FT interrupt output can be used to generate an external interrupt when the RTC register values
match user programmed alarm values. The interrupt is always available while the device is powered from
the system supply and can be programmed to occur when in the battery-backed state to serve as a system
wake-up. Either the IRQ/FT or RST outputs can also be used as a CPU watchdog timer, CPU activity is
monitored and an interrupt or reset output will be activated if the correct activity is not detected within
programmed limits. The DS1556 power-on reset can be used to detect a system power down or failure
and hold the CPU in a safe reset state until normal power returns and stabilizes; the RST output is used
for this function.
The DS1556 also contains its own power-fail circuitry, which automatically deselects the device when the
VCC supply enters an out of tolerance condition. This feature provides a high degree of data security
during unpredictable system operation brought on by low VCC levels.
PACKAGES
The DS1556 is available in two packages (32-pin DIP and 34-pin PowerCap module). The 32-pin DIP
style module integrates the crystal, lithium energy source, and silicon all in one package. The 34-pin
PowerCap module board is designed with contacts for connection to a separate PowerCap (DS9034PCX)
that contains the crystal and battery. This design allows the PowerCap to be mounted on top of the
DS1556P after the completion of the surface mount process. Mounting the PowerCap after the surface
mount process prevents damage to the crystal and battery due to the high temperatures required for solder
reflow. The PowerCap is keyed to prevent reverse insertion. The PowerCap Module board and PowerCap
are ordered separately and shipped in separate containers. The part number for the PowerCap is
DS9034PCX.
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DS1556 1M, Nonvolatile, Y2K-Compliant Timekeeping RAM
Figure 1. Block Diagram
Maxim
DS1556
Table 1. Operating Modes
VCC
VCC > VPF
VSO < VCC
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