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Maxim > Design Support > Technical Documents > Application Notes > Memory > APP 202
Keywords: NVSRAM, non-volatile, nonvolatile static random access memory, NV SRAMs, nvsram,
DS1220, DS1225, DS1230 MK48Z08, MK48z18, Dallas Semiconductor, SmartSocket, smartsocket, LPM
APPLICATION NOTE 202
NV SRAM Frequently Asked Questions
May 14, 2002
Abstract: This application note discusses theory of operation and application of NV SRAMs such as the
DS1220, DS1225, and DS1230. First it discusses NV SRAM module construction, with an overview of
the battery, controller, and SRAM that is used in a typical device. Application information regarding
interconnects to popular 8-bit Motorola® and Intel® bus structures is shown in block diagram form.
Answers to common questions regarding issues found during the design, test, manufacture, and use of
NV SRAMs in electronic systems is explained in detail. Information on some older and obsolete parts is
discussed with recommendations on pin-for-pin replacements with more contemporary devices.
What Is an NV SRAM?
How Do I Interface to an NV SRAM?
Can You Turn the Freshness Seal Back On Once Power Has Been Applied?
Can You Measure the Battery Voltage of an NV SRAM?
Since Flash Memory Is a Lot Cheaper, Why Not Use It Instead of NV SRAM?
Are 3.3V Parts Available?
Are Maxim NV SRAMs UL Recognized?
What Other Functions Are Available on NV SRAMs?
What Replacement Parts Should I Use for the DS16** Series of NV SRAMs?
Why Is the Battery in my DS1213 SmartSocket Dead?
I Replaced My Standard SRAM with an NV SRAM and Now My System Doesn't Work at All. What
Caused This?
Why Am I Getting Data Corruption in My NV SRAM?
What's a DS1235?
What Does the "-200" Mean, and Why Are Those Products Unavailable?
What's an LPM?
Are Any NV SRAMs Not Recommended for Future Designs?
What Is an NV SRAM?
A nonvolatile static random access memory (NV SRAM) is a type of computer memory that maintains its
data when power is shut off. NV SRAMs store digital information like system configuration or temporarily
store transient digital data, such as what passes through a telecom router, so that it can be recovered in
case of a power failure.
An NV SRAM is a nonvolatile memory module built using a standard SRAM, an integrated circuit (IC)
controller with a battery switchover circuit, and a lithium battery. All of these components are mounted on
a circuit board and encapsulated in a plastic tub. The example below (Figure 1) is pinned out to match
the footprint and pinout of a JEDEC-standard SRAM so that the two can be used interchangeably.
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