Most MCUs (microcontrollers) are not equipped with sufficient RAM space for execution. The common alternatives are all sub-optimal: either upgrade to a microcontroller with higher density embedded RAM at a significant premium, or go with an external serial EEPROM with limited write endurance and serial  access.



Smart Card

SRAM Replacement


EMRAM Extension of MCU


EMRAM is a fast memory (cycle time <70ns), is nonvolatile and has unlimited write / read endurance. It is in effect RAM and nonvolatile storage in the same device. Because of this unique combination, EMRAM is a perfect choice as the external supplemental memory to a MCU. The user can decide on the segmentation of volatile and nonvolatile data within a single EMRAM device. To further optimize the performance of the MCU-EMRAM combination, the user can assign variables that require high speed and frequent access to the embedded RAM.

This document outlines some key memory considerations facing the user today, and how EMRAM can be integrated into the system.

Memory Applications
As a RAM-extension of the MCU, EMRAM can be used in all of the following memory applications:

Sample Storage
This is the place where the software collects data for later processing. This is a write intensive application with high data-sample rate that rapidly accumulates write cycles. In certain applications, data is not collected at sufficiently high rate because of the bottleneck in memory speed.

EEPROM is not suitable for data storage because of poor write endurance (100,000-1,000,000 write cycles), slow write time (~10ms) and high write power (12V). EMRAM overcomes all this. It has unlimited write endurance, writes with no delay and consumes little power (write voltage 5V).

In an Analog/Digital conversion, EMRAM easily supports data sampling at less than 1µs interval (1MHz) for continuous operation at 365 days / 24 hours while EEPROM and other memory alternatives cannot.


Scratchpad Buffer
This is a general purpose memory block that is subject to random write operations. Endurance over long periods is unpredictable and is therefore a key consideration. Because write operations is essentially random, the user do not want to employ a memory with a limited endurance performance. As EMRAM has unlimited write endurance, it is well suited to even the most demanding scratch pad buffer needs.


Circular Buffer
This is a memory block where software uses each memory location in sequence until it reaches the end of the block before starting at the beginning of the address range. The write operations normally occur periodically and with a fixed buffer size. It is therefore the least demanding application in terms of endurance performance.


Microcontroller Interface
In a system that already employs an external EEPROM to a MCU, adding EMRAM requires simply a replacement of the EEPROM with a pin-compatible serial EMRAM with the desired memory density. Write data to new memory locations as though the serial device is a RAM. When a MCU does not support serial RAM, the user application must move data from EMRAM to the embedded RAM locations before execution.The user will also have to modify the system to take advantage of EMRAM’s higher speed by acknowledge polling and removing any delays.

In a system that does not currently use external EEPROM, the EMRAM device must be designed in. Because EMRAM is available in both serial (I2C, Microwire, SPI) and parallel (RAM) formats, it should be compatible with existing MCU interfaces and direct connection is possible. If software emulation of the interface is required, the user can obtain the appropriate software from major MCU vendors who maintain a large library of such software.

Information furnished is believed to be accurate and reliable. However, NLSC assumes no responsibility for the consequences of use of such information nor for any infringement of patents or other rights of third parties which may result from its use. No license is granted by implication or otherwise under any patent or patent rights of NLSC. Specifications mentioned in this publication are subject to change without notice. This publication supercedes and replaces all information previously supplied. NLSC products are not authorized for use as critical components in life support devices or systems without express written approval of NLSC.

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