19-5497; Rev 9/10
DS1554
256k, Nonvolatile, Y2K-Compliant
Timekeeping RAM
www.maxim-ic.com
FEATURES
PIN CONFIGURATIONS
Integrated NV SRAM, Real-Time Clock
(RTC), Crystal, Power-Fail Control Circuit,
and Lithium Energy Source
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
BCD-Coded Year, Month, Date, Day, Hours,
Minutes, and Seconds with Automatic LeapYear Compensation Valid Up to the Year
2100
Battery Voltage-Level Indicator Flag
Power-Fail Write Protection Allows for ±10%
VCC Power-Supply Tolerance
Lithium Energy Source is Electrically
Disconnected to Retain Freshness Until
Power is Applied for the First Time
Also Available in Industrial Temperature
Range: -40°C to +85°C
TOP VIEW
RST
N.C.
A14
A12
A7
A6
A5
A4
A3
A2
A1
1
Maxim
2
3 DS1554
4
5
6
7
8
9
10
11
12
32
31
30
29
28
27
26
25
24
23
22
21
VCC
N.C.
DQ0
13
20
DQ6
DQ1
DQ2
14
19
DQ5
15
18
DQ4
GND
16
17
DQ3
A0
IRQ/FT
WE
A13
A8
A9
A11
OE
A10
CE
DQ7
Encapsulated DIP
IRQ/FT
N.C.
N.C.
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
DS1554
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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DS1554 256k, Nonvolatile, Y2K-Compliant Timekeeping RAM
PIN DESCRIPTION
A0–A14
DQ0–DQ7
IRQ/FT
RST
CE
OE
WE
VCC
GND
N.C.
X1, X2
VBAT
- Address Inputs
- 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
DS1554-70+
DS1554-70IND+
DS1554P-70+
DS1554P-70IND+
DS1554W-120+
DS1554W-120IND+
DS1554WP-120+
DS1554WP-120IND+
TEMP RANGE
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
VOLTAGE
(V)
5.0
5.0
5.0
5.0
3.3
3.3
3.3
3.3
PIN-PACKAGE
TOP MARK**
32 EDIP (0.740a)
32 EDIP (0.740a)
34 PowerCap*
34 PowerCap*
32 EDIP (0.740a)
32 EDIP (0.740a)
34 PowerCap*
34 PowerCap*
DS1554+070
DS1554+070 IND
DS1554P+70
DS1554P+70 IND
DS1554W+120
DS1554W+120 IND
DS1554WP+120
DS1554WP+120 IND
+Denotes a lead(Pb)-free /RoHS-compliant package.
*DS9034-PCX+ or DS9034I-PCX+ required (must be ordered separately).
**The top mark will include a “+” on lead-free devices. An “IND” anywhere on the top mark indicates an industrial temperature grade device.
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DS1554 256k, Nonvolatile, Y2K-Compliant Timekeeping RAM
DESCRIPTION
The DS1554 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 32k x 8 nonvolatile static RAM. User
access to all registers within the DS1554 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
binary-coded decimal (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; this occurs regardless of external registers settings to guarantee that accurate RTC
information is always maintained.
The DS1554 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
wakeup. 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 DS1554 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 DS1554 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 DS1554 is available in two packages (32-pin encapsulated 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 DS1554P 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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DS1554 256k, Nonvolatile, Y2K-Compliant Timekeeping RAM
Figure 1. Block Diagram
Maxim
DS1554
Table 1. Operating Modes
VCC
VCC > VPF
VSO < VCC
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