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PDF DS1556 Data sheet ( Hoja de datos )
| Número de pieza | DS1556 | |
| Descripción | 1M / Nonvolatile / Y2K-Compliant Timekeeping RAM | |
| Fabricantes | Dallas Semiconducotr | |
| Logotipo |  |
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www.maxim-ic.com
DS1556
1M, Nonvolatile, Y2K-Compliant
Timekeeping RAM
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 CONFIGURATIONS
TOP VIEW
RST
A16
A14
A12
A7
A6
A5
A4
A3
A2
A1
A0
DQ0
DQ1
DQ2
GND
1 32
2 SemiDcaolnladsuctor31
3 DS1556 30
4 29
5 28
6 27
7 26
8 25
9 24
10 23
11 22
12 21
13 20
14 19
15 18
16 17
VCC
A15
IRQ/FT
WE
A13
A8
A9
A11
OE
A10
CE
DQ7
DQ6
DQ5
DQ4
DQ3
Encapsulated DIP
IRQ/FT
A15
A16
RST
VWCCE
OE
CE
DQ7
DQ6
DQ5
DQ4
DQ3
DQ2
DQ1
DQ0
GND
1
2
Dallas
34
33
3
Semiconductor
32
4
5
DS1556
31
30
6 29
7 28
8 27
9 26
10 25
11 24
12 23
13 22
14 21
15 20
16
17
X1 GND VBAT X2
19
18
PowerCap® Module Board
(Uses DS9034PCX PowerCap)
N.C.
N.C.
A14
A13
A12
A11
A10
A9
A8
A7
A6
A5
A4
A3
A2
A1
A0
PowerCap is a registered trademark of Dallas Semiconductor.
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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REV: 101804
1 page  
DS1556 1M, Nonvolatile, Y2K-Compliant Timekeeping RAM
BATTERY LONGEVITY
The DS1556 has a lithium power source that is designed to provide energy for the 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 DS1556 continuously for the life of the equipment in which it is
installed. For specification purposes, the life expectancy is 10 years at 25°C with the internal clock
oscillator running in the absence of VCC. Each DS1556 is shipped from Dallas Semiconductor with its
lithium energy source disconnected, guaranteeing full energy capacity. When VCC is first applied at a
level greater than VPF, the lithium energy source is enabled for battery backup operation. Actual life
expectancy of the DS1556 will be much longer than 10 years since no internal battery energy is
consumed when VCC is present.
INTERNAL BATTERY MONITOR
The DS1556 constantly monitors the battery voltage of the internal battery. The Battery Low Flag (BLF)
bit of the Flags Register (B4 of 1FFF0h) is not writable and should always be a 0 when read. If a 1 is ever
present, an exhausted lithium energy source is indicated and both the contents of the RTC and RAM are
questionable.
POWER-ON RESET
A temperature compensated comparator circuit monitors the level of VCC. When VCC falls to the power
fail trip point, the RST signal (open drain) is pulled low. When VCC returns to nominal levels, the RST
signal continues to be pulled low for a period of 40 ms to 200 ms. The power-on reset function is
independent of the RTC oscillator and thus is operational whether or not the oscillator is enabled.
CLOCK OPERATIONS
Table 2 and the following paragraphs describe the operation of RTC, alarm, and watchdog functions.
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5 Page 
DS1556 1M, Nonvolatile, Y2K-Compliant Timekeeping RAM
DC ELECTRICAL CHARACTERISTICS
(VCC = 3.3V ±10%, Over the Operating Range.)
PARAMETER
SYMBOL
CONDITIONS
Active Supply Current
TTL Standby Current
(CE = VIH)
CMOS Standby Current
(CE ³ VCC - 0.2V)
Input Leakage Current
(Any Input)
Output Leakage Current
(Any Output)
Output Logic 1 Voltage
(IOUT = -1.0 mA)
Output Logic 0 Voltage
ICC
ICC1
ICC2
IIL
IOL
VOH
VOL1
VOL2
(Notes 2, 3)
(Notes 2, 3)
(Notes 2, 3)
(Note 1)
IOUT = 2.1 mA, DQ0–7
Outputs (Note 1)
IOUT = 7.0 mA, IRQ/FT
and RST Outputs
(Notes 1, 5)
Write Protection Voltage
VPF (Note 1)
Battery Switchover Voltage
VSO (Notes 1,4)
MIN
TYP
20
2
MAX
30
6
UNITS
mA
mA
1 4 mA
-1 +1 mA
-1 +1 mA
2.4 V
0.4 V
0.4
2.75
VBAT
or
VPF
2.97
V
V
V
Figure 5. Read Cycle Timing Diagram
11 of 20
11 Page | ||
| Páginas | Total 20 Páginas | |
| PDF Descargar | [ Datasheet DS1556.PDF ] | |
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