When choosing a serial EEPROM, there is a balancing act between cost and density, but the system software will usually drive this requirement. Usually the amount of memory required to complete a project is estimated before the design is completed. The final density purchased is usually 50% larger to allow for future growth.

To better illustrate the process of selecting a specific EEPROM device, here is an example of the types of questions that come up in the design phase:

• Does the microcontroller have a programmable serial port that can support I²C, SPI, Microwire or UNI/O^® serial buses?
• How many spare I/O ports on the microcontroller are available for use by the EEPROM?
  • Is your microcontroller pin limited?
  • Is it cheaper to switch to a bigger microcontroller or reduce the I/O ports required to interface with the serial EEPROM?
  • Do you need to use less I/O pins with memory on the microcontroller to free up the extra I/O pins for other applications?
• Are there any other peripherals in the system design that use a serial interface such as I²C, SPI or Microwire?
  • If no serial ports are available, will the serial interface be emulated by bit banging several I/O ports?
• How much memory will be required to complete the project and will it be necessary to upgrade to a larger memory size in the future?
  • If more memory is needed, will a larger package impact the design?
  • If more memory is needed will cascading serial EEPROMs be a viable option
• Is the bus speed known so that a bus type can be selected?
• If there is a limitation of I/O ports, will the slower speeds of the I²C or UNI/O bus meet the system requirements since they use the fewest I/O ports, two and one respectively?
• Are there any space constraints in the application that dictate a smaller package or die/wafer?
• Is there a minimum or maximum voltage or operating temperature requirement?
  

In many cases, the application notes and technical briefs you read will point you directly to the part you should use. Finally, contact your contact our local Microchip representative and discuss your findings with one of our knowledgeable sales staff or Field Applications Engineers (FAEs). They would be happy to help you with your Serial EEPROM selection.