19-5501; Rev 9/10
DS1557
4Meg, 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
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 Leap
Year 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
PIN CONFIGURATION
TOP VIEW
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
DS1557
X1
GND VBAT
X2
34
33
32
31
30
29
28
27
26
25
24
23
22
21
20
19
18
A18
A17
A14
A13
A12
A11
A10
A9
A8
A7
A6
A5
A4
A3
A2
A1
A0
PowerCap Module Board
(Uses DS9034PCX PowerCap)
PIN DESCRIPTION
A0–A18
DQ0–DQ7
IRQ/FT
RST
CE
OE
WE
VCC
GND
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
- Crystal Connection
- Battery Connection
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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DS1557 4Meg, Nonvolatile, Y2K-Compliant Timekeeping RAM
ORDERING INFORMATION
PART
TEMP RANGE
DS1557P-70+
DS1557P-70IND+
DS1557WP-120+
DS1557WP-120IND+
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
3.3
3.3
PIN-PACKAGE
TOP MARK**
34 PowerCap*
34 PowerCap*
34 PowerCap*
34 PowerCap*
DS1557P+70
DS1557P+70 IND
DS1557WP+120
DS1557WP+120 IND
+ Denotes a lead(Pb)-free/RoHS-compliant package.
*DS9034PCX+ or DS9034I-PCX+ (PowerCap) required. Must be ordered separately.
*An “IND” on the top mark denotes an industrial temperature grade device.
DESCRIPTION
The DS1557 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 512k x 8 nonvolatile static RAM. User
access to all registers within the DS1557 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; this occurs regardless of external registers settings to guarantee that accurate RTC
information is always maintained.
The DS1557 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 DS1557 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 DS1557 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.
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DS1557 4Meg, Nonvolatile, Y2K-Compliant Timekeeping RAM
Figure 1. Block Diagram
Maxim
DS1557
Table 1. Operating Modes
VCC
VCC > VPF
VSO < VCC
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