Options for data storage

[chris-s]

I'm working on a project that will probably end up on a 20x1 or 40x1 which is currently using some of the eeprom to store data over a period of time. It doesn't accumulate data, the volume of data is fixed, it just changes over time and easily fits within the 256 bytes available.

I would like to be able to update the application from time to time to fine-tune the algorithms without loosing the data. Whats the best method of doing this?

Chris

 

[inglewoodpete]

As you are probably aware, most PICAXE chips have their EEPROM data overwritten when they are reprogrammed. There are 2 methods that come to mind.

The first is to have a separate EEPROM chip connected to the PICAXE. Depending on how much data you need to store, a second smaller PICAXE like an 08M may be a simple hardware solution.

The second is more tedious but requires no extra hardware. At startup the PICAXE needs to run a quick loop routine that outputs the required contents of its internal EEPROM to the programming link or other serial port. Under normal working conditions, the data is output to nowhere. When you need to reprogramme the chip, you use some sort of terminal program to receive and store the data when you force the PICAXE to reboot. The data would then have to be massaged and merged into the source code, incorporating "Data" or "EEPROM" statements.

 

[womai]

I'd recommend using an external EEPROM. The Microchip 24LCxx series is perfect for that (you can use a small, cheap one like the 24LC32) and doesn't take much board space or components - just the chip, plus 2 pullup resistors (2 - 5 kOhms works fine) to Vcc for the SDA and SCK lines. Once you get the hang of it, you'll find using those chips a breeze.

Wolfgang

 

[chris-s]

Thanks for the replies guys, think I'll take a look at the 24LC32 tho it also occured to be last night that one of the other 'chips' in the project is an LCD driver chip interfaced over i2c that I think has some spare eeprom, so that might also be an option. The 24LC32 is a good excuse to look at something new anyhow.

Cheers

Chris