Question on ext. EEPROM and 08M

[Mx5Daz]

Is there a way of using an external EEPROM with a PICAXE-08M?

I know I can use an 18X and i2c a lot more easily but the due to the lower cost of these chips I'm experimenting to see if I can use an 08M.

The EEPROM I want to use for development purposes is the 24LC512. If there are other more suitable EEPROMs I'm all ears, but that's what I have to work with at the moment.

I'm sure this has been covered before but I promise I did search. Nothing came up that seemed to cover it though.

Cheers

Darren

 

[hippy]

Have a read of the following thread which discusses some of the issues of I2C with 08M -

http://www.picaxeforum.co.uk/showthread.php?t=13792

I've included an 08M driver for byte addressed I2C Eeprom ( up to 24LC16 ) but going to word addressed means updating the code. Not sure when I will have the time to do that though you should be able to do it yourself.

The current easy options then are; 08M plus smaller I2C Eeproms, 18X and upwards for larger I2C Eeproms.

 

[westaust55]

Untested by myself, but a possible alternative to an i2c Serial EEPROM might be an SPI Serial EEPROM. (eg 25LC512)

http://ww1.microchip.com/downloads/en/DeviceDoc/22065B.pdf

The bit-bash code for the SHIFTIN and SHIFTOUT commands in the PICAXE Manual 2 could be adapted.

would require 3 wires instead of 2 however.

Whether you could still get this usefully into an 08M and have program space remaining for your application ?????

 

[Mx5Daz]

Thanks for the input guys.

The program itself is quite simple, the interface code would take up most of it.

I think I'm rapidly running out of i/o though, so I don't think it's looking like a viable option. No, in fact it won't because I need minimum 2 ADC inputs, plus EEPROM interface and DAC out, it just won't all squeeze into an 08M.

A 14M might work but since I don't have any I'd have to buy one to experiment with and that's kind of negating the point. Going up from that just gets me closer cost-wise to the 18X/20X2 that I already have.

I think I'll make my life easier and use an 18X or 20X2. They just seem like overkill for the task!

Hippy: I might have a go at your i2c code at some point to see if I can get it to work with word addressed chips, just for the sake of interest. There used to be a trick on old 8bit computers where concatenating lines of code would take less space by a couple of bytes. Does this trick work with PICAXE? I'd guess not since it's compiled code not interpreted but it's worth an ask!

Thanks for the help.

Daz

 

[hippy]

I tried tweaking the code for word addressed Eeprom but it just doesn't seem to pss all tests and I don't have the time to investigate.

No, concatenating lines doesn't save any memory use on the PICAXE. Turning mutliple math manipulating lines into a single line usually will.