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Design with serial EEPROM devices

Posted: 01 Jun 2007 ?? ?Print Version ?Bookmark and Share

Keywords:EEPROM design? EEPROM devices? serial EEPROM?

An estimated 5 billion serial EEPROM units are produced worldwide each year, making it one of the most commonly used non-volatile memory devices in the industry today. Serial EEPROM devices are easy to use, and they integrate into a variety of applications. Available with varying capacities, interface protocols, voltages and temperature ranges, the parts are used in applications running the gamut from automotive to medical and consumer goods. Here are some do's and don'ts for designing with serial EEPROM devices.

Do

? Pick the right interface protocol for the application. The most popular protocols are I?C, SPI and Microwire, each having advantages and disadvantages for specific applications.

? Use robust design techniques. This includes following the manufacturer's recommended usage instructions regarding decoupling capacitor sizes and pull-up/pull-down resistor values. Avoid tying the serial EEPROM VDD pin to an output pin on your MCUyou won't save much current, and you will cause unnecessary headaches if the power is removed during a write cycle.

? Take advantage of the tools that manufacturers may have to help you design with their devices. These can be programmers, such as Microchip's SEEVAL 32, Verilog/VHDL models of the device or pre-tested code for your MCU. Review application notes provided by the serial EEPROM device manufacturer that might be specific to the product you chose. These tips and tricks, and recommended usage notes can save time or costly firmware workarounds for apparent problems.

? Take advantage of hardware interface peripherals on your MCU, such as SPI or I?C ports. These can make code development less tedious and will generally result in a faster application with more compact code, leaving room to add other features and minimizing the cost of your MCU.

Don't

  • Slow down writes. Use the page-write feature, if your product has one. This lets you write a full page of data at once by loading the page with data and initiating the write cycle (from 16bytes to 256bytes). All bytes in the page will be written at the same time.

  • Leave your serial EEPROM device unprotected. Protect against accidental array writes by using hardware write-protect pins, write-disable commands, block protection and other techniques.

  • Presume that the serial EEPROM will stop working when your controller does. Most serial EEPROMs are designed to execute a write at low voltagestypically, at less than 1.8V. For example, if your MCU's voltage drops below 2.5V and the controller chip operates erratically, executing unintended code or write instructions, the serial EEPROM device may interpret those commands as valid and execute them. Data corruption can result. Design your system so that during power-up and -down, the controller chip is in reset until the system voltage is stable.

  • Wear out your serial EEPROM device. It is possible to wear out a serial EEPROM device if you write to it several million times. If you plan to rewrite to the device frequently, learn about the device's endurance characteristics. Endurance modeling tools can help you identify product warranty issues that might result from the number of writes you plan.

- David Wilkie
Engineering Manager, Memory Products Division
Microchip Technology Inc.




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