External memory

[Anon_LG]

For my next project I will be using a bare attiny, most likely the atiny 85 or 84. I need long term data storage, internal EEPROM is not an option due to finite lifetime and internal RAM is not an option due to the requirement that the microcontroller is on constantly. I have two options, one is that I use external EEPROM as if it faults it can be replaced with a new one or I use external RAM as this has extremely low standby current draw. Does anyone have any suggestions? I have looked at a few options such as https://www.sparkfun.com/products/525, the thing that is confusing me with this one is that when I research i2c on the attiny it says pull up resistors MUST be used, however user Alvinx (on the Sparkfun comments) says pull up resistors are not required. I have also considered this: http://www.hobbytronics.co.uk/23k256-sram?keyword=memory however I am unsure whether tinySPI (required for attiny to interface with SPI devices) supports 20Mhz operation. Help is greatly appreciated as my project is not do-able if this is not resolved.

Thanks,

 

[Harald Kapp]

Whether to use SRAM or EEPROM depends on your application. Consider these main differences:

RAM: read and write infinite times / EEPROM: read infinite times, write only a limited number of cycles (10^5...10^6, see datasheet).
RAM: requires a battery / EEPROM: no battery required, da will survive total loss of power.

As to I2C vs, SPI, here is a comparison of the two.Personally I think SPI is easier to handle, too, and should be able to handle higher transfer rates than I2C (as confirmed by the linked article). If you use I2C a pull-up is typically required. You will find (and in fact you did) references to I2C without using pull-ups, but that is imho no good design. You may get away with using internal pull-up offered by some controllers on their I/O pins.