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Topic: resistances on EEPROM wiring? (Read 1 time) previous topic - next topic

madepablo

Mar 27, 2011, 01:19 pm Last Edit: Mar 27, 2011, 01:23 pm by madepablo Reason: 1
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/

Here is an example where they say that is necessary in both i2C connections:
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

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!

graynomad

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


Rob Gray aka the GRAYnomad www.robgray.com

madepablo

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!

Coding Badly

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

madepablo


madepablo

Tested!

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

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