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Maxim > Products > [Real-Time Clocks] 
DS1556, DS1556P
1M, Nonvolatile, Y2K-Compliant Timekeeping RAM


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Status
Part Number Status
DS1556 Active: In Production. But some versions of the family are No Longer Available. See Ordering Information.
DS1556P Active: In Production. But some versions of the family are No Longer Available. See Ordering Information.

Data Sheet
FULL DATA SHEET (PDF, 388kB)
Download this datasheet in PDF formatDownload   Send this datasheet to any email addressE-Mail

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 (active-low IRQ/FT) and reset (active-low RST) outputs which can be used to control CPU activity. The active-low 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 active-low IRQ/FT or active-low 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 active-low 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.

This product contains lithium-metal batteries. See applicable regulations for transport requirements for batteries in equipment.

Key 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
  • Underwriters Laboratories (UL®) Recognized

Key Specifications:  Timekeeping & Real-Time Clocks
Part Number Functions Date/ Time Format Interface VSUPPLY
(V)		 Memory Type Memory Size
(Bytes)		 Time of Day Alarms Price
hh = sec/100 See Notes
DS1556  Watchdog Timekeeper YYYY-MM-DD/ HH:MM:SS Bytewide
3.3
5
 NV SRAM 128K 1 $15.75 @1k
See All Timekeeping & Real-Time Clocks (80)

Diagram
DS1556, DS1556P: Block Diagram
Block Diagram

Application Notes
  		• Application Note 504: Design Considerations for Dallas Semiconductor Real-Time Clocks - DS1556
  		• Application Note 507: PowerCap Package Allows for Density Upgrades, Surface Mount Assembly - DS1556, DS1556
  		• Application Note 520: Using a Watchdog Timekeeping RAM with a Microcontroller - DS1556

    Design Guides
  		• Real-Time Clocks (PDF)

    Reliability Reports
  		• Reliability Report: DS1556.pdf DS1556P.pdf
  		• Underwriters Laboratories (UL®) Recognized

    Software/Models
    none

    Ordering Information
    Notes:

    1. Other options and links for purchasing parts are listed at: http://www.maxim-ic.com/sales.
    2. Didn't Find What You Need? Ask our applications engineers. Expert assistance in finding parts, usually within one business day.
    3. Part number suffixes: T or T&R = tape and reel;+ = RoHS/lead-free;# = RoHS/lead-exempt. More: SeeFull Data Sheet or Part Naming Conventions.
    4. * Some packages have variations, listed on the drawing. "PkgCode/Variation" tells which variation the product uses. Note that "+", "#", "-" in the part number suffix describes RoHS status. Package drawings may show a different suffix character.


    Devices: 1-17 of 17

    DS1556 Free
    Sample    		 Buy Status Recommended Replacement
    Package: TYPE PINS FOOTPRINT
      DRAWING CODE/VAR *
    		Temp RoHS/Lead-Free?
    Materials Analysis
    DS1556-70-W     N/A No Longer Available DS1556-70+

    Land Pattern: Not Available

    		0°C to +70°C See data sheet
    DS1556W-120     N/A No Longer Available DS1556W-120+
    		 EDIP;32 pin;707 mm²
    Outline Drawing: 21-0245 (PDF)
    Land Pattern: Not Available
    Use pkgcode/variation: MDF32-1*
    		0°C to +70°C RoHS/Lead-Free: No
    Materials Analysis
    DS1556-70IND     N/A No Longer Available DS1556-70IND+
    		 EDIP;32 pin;707 mm²
    Outline Drawing: 21-0245 (PDF)
    Land Pattern: Not Available
    Use pkgcode/variation: MDF32-1*
    		-40°C to +85°C RoHS/Lead-Free: No
    Materials Analysis
    DS1556W-120IND     N/A No Longer Available DS1556W-120IND+
    		 EDIP;32 pin;707 mm²
    Outline Drawing: 21-0245 (PDF)
    Land Pattern: Not Available
    Use pkgcode/variation: MDF32-1*
    		-40°C to +85°C RoHS/Lead-Free: No
    Materials Analysis
    DS1556-70  
    		Active
    		EDIP;32 pin;707 mm²
    Outline Drawing: 21-0245 (PDF)
    Land Pattern: Not Available
    Use pkgcode/variation: MDF32-1*
    		0°C to +70°C RoHS/Lead-Free: No
    Materials Analysis
    DS1556-70+  
    		Active
    		EDIP;32 pin;707 mm²
    Outline Drawing: 21-0245 (PDF)
    Land Pattern: Not Available
    Use pkgcode/variation: MDF32+1*
    		0°C to +70°C RoHS/Lead-Free: Lead Free
    Materials Analysis
    DS1556W-120+  
    		Active
    		EDIP;32 pin;707 mm²
    Outline Drawing: 21-0245 (PDF)
    Land Pattern: Not Available
    Use pkgcode/variation: MDF32+1*
    		0°C to +70°C RoHS/Lead-Free: Lead Free
    Materials Analysis
    DS1556-70IND+    
    		Active
    		EDIP;32 pin;707 mm²
    Outline Drawing: 21-0245 (PDF)
    Land Pattern: Not Available
    Use pkgcode/variation: MDF32+1*
    		-40°C to +85°C RoHS/Lead-Free: Lead Free
    Materials Analysis
    DS1556W-120IND+    
    		Active
    		EDIP;32 pin;707 mm²
    Outline Drawing: 21-0245 (PDF)
    Land Pattern: Not Available
    Use pkgcode/variation: MDF32+1*
    		-40°C to +85°C RoHS/Lead-Free: Lead Free
    Materials Analysis
    DS1556WP-120    
    		Active
    		PCAP;34 pin;597 mm²
    Outline Drawing: 21-0246 (PDF)
    Land Pattern: Not Available
    Use pkgcode/variation: PC2-6*
    		0°C to +70°C RoHS/Lead-Free: No
    Materials Analysis
    DS1556WP-120+  
    		Active
    		PCAP;34 pin;597 mm²
    Outline Drawing: 21-0246 (PDF)
    Land Pattern: Not Available
    Use pkgcode/variation: PC2+6*
    		0°C to +70°C RoHS/Lead-Free: Lead Free
    Materials Analysis
    DS1556WP-120IND+    
    		Active
    		PCAP;34 pin;597 mm²
    Outline Drawing: 21-0246 (PDF)
    Land Pattern: Not Available
    Use pkgcode/variation: PC2+6*
    		-40°C to +85°C RoHS/Lead-Free: Lead Free
    Materials Analysis
    DS1556WP-120IND    
    		Active
    		PCAP;34 pin;597 mm²
    Outline Drawing: 21-0246 (PDF)
    Land Pattern: Not Available
    Use pkgcode/variation: PC2-6*
    		-40°C to +85°C RoHS/Lead-Free: No
    Materials Analysis
    DS1556P Free
    Sample    		 Buy Status Recommended Replacement
    Package: TYPE PINS FOOTPRINT
      DRAWING CODE/VAR *
    		Temp RoHS/Lead-Free?
    Materials Analysis
    DS1556P-70+  
    		Active
    		PCAP;34 pin;597 mm²
    Outline Drawing: 21-0246 (PDF)
    Land Pattern: Not Available
    Use pkgcode/variation: PC2+6*
    		0°C to +70°C RoHS/Lead-Free: Lead Free
    Materials Analysis
    DS1556P-70IND+    
    		Active
    		PCAP;34 pin;597 mm²
    Outline Drawing: 21-0246 (PDF)
    Land Pattern: Not Available
    Use pkgcode/variation: PC2+6*
    		-40°C to +85°C RoHS/Lead-Free: Lead Free
    Materials Analysis
    DS1556P-70IND     N/A No Longer Available DS1556P-70IND+
    		 PCAP;34 pin;597 mm²
    Outline Drawing: 21-0246 (PDF)
    Land Pattern: Not Available
    Use pkgcode/variation: PC2-6*
    		-40°C to +85°C RoHS/Lead-Free: No
    Materials Analysis
    DS1556P-70  
    		Active
    		PCAP;34 pin;597 mm²
    Outline Drawing: 21-0246 (PDF)
    Land Pattern: Not Available
    Use pkgcode/variation: PC2-6*
    		0°C to +70°C RoHS/Lead-Free: No
    Materials Analysis

    More Information
  		• Other Watchdog Clocks

    Related Products
    DS9034PCX PowerCap with Crystal

    More Like This: View Product Families for Similar Products

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    2005-07-15
    This page last modified: 2009-09-24


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