Arduino Forum

Using Arduino => Storage => Topic started by: madepablo on Mar 27, 2011, 01:19 pm

Title: resistances on EEPROM wiring?
Post by: madepablo on Mar 27, 2011, 01:19 pm
I want to use an 24LC256 EEPROM. I take a look to the data sheet, on internet and in this forum about how to wire it, and i observed differences about f you resistances in SDA and SCL connections of the EEPROM to Arduino board.

Here is an example where they do not use resistances:
http://kans01.wordpress.com/2008/03/13/usando-una-memoria-eeprom-desde-arduino/ (http://kans01.wordpress.com/2008/03/13/usando-una-memoria-eeprom-desde-arduino/)

Here is an example where they say that is necessary in both i2C connections:
http://electronicapractica.crearblog.com/tag/24lc256/ (http://electronicapractica.crearblog.com/tag/24lc256/)

And the datasheet only say something about resistances in SDA (but do not say anything about resistances in SCL):
http://www.datasheetcatalog.com/datasheets_pdf/2/4/L/C/24LC256.shtml (http://www.datasheetcatalog.com/datasheets_pdf/2/4/L/C/24LC256.shtml)

So, my questions are:

Is it really necessary resistances on i2c with this eeprom? In both connections (or only on SDA)? What resistance value should i use?

May be they are easy questions, but i donĀ“t want to burn my arduino duemilanove...
Thanks for your help!
Title: Re: resistances on EEPROM wiring?
Post by: graynomad on Mar 27, 2011, 01:24 pm
AFAIK you always need pullup resistors with I2C, it's an open collector/drain bus, it's possible the first example used the internal ones.

As for the value for a single device and short line it probably doesn't matter much, try 4k7.

______
Rob


Title: Re: resistances on EEPROM wiring?
Post by: madepablo on Mar 27, 2011, 02:02 pm
Great. Thanks Graynomad!

I will try it.

by the way, i just saw this other example using 4K7 resistances in both SDA and SCL, more over a 0.1uF ceramic capacitor between +5V and GND of the EEPROM. I suposse that to stablilize the power.

Thanks!
Title: Re: resistances on EEPROM wiring?
Post by: Coding Badly on Mar 28, 2011, 08:24 am
more over a 0.1uF ceramic capacitor between +5V and GND of the EEPROM. I suposse that to stablilize the power.


http://www.thebox.myzen.co.uk/Tutorial/De-coupling.html
Title: Re: resistances on EEPROM wiring?
Post by: madepablo on Mar 28, 2011, 02:57 pm
Thanks Coding Badly!!
Title: Re: resistances on EEPROM wiring? [SOLVED]
Post by: madepablo on Apr 04, 2011, 11:46 pm
Tested!

It works perfectly with 4K7 pull up resistances on SDA and SCL I2C pins.
Thanks guys!