how do use i2c on arduino with out pull-up ?

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Apr 9, 2012. 3:08 AM

steveastrouk says:

You don't set the pull up/downs in the output mode on an AVR, you can only do it for input mode.

Apr 9, 2012. 1:27 PM

iceng says:

+1
Output means a pin on a digital IC like a Pic, Arduino or AVR
is FORCED High or low by an internal process and a "pull up"
is non sequitur when compared to a Real output pin.

Of course you could be thinking of an open collector output like some
sensors that need a pull up resistor.

That does not occur ever in the land of micro-processors :-)

A

Apr 9, 2012. 8:03 PMact casual (author) says:

(removed by author or community request)

Apr 10, 2012. 1:58 AM

steveastrouk says:

You're using the onboard TWI aren't you ?

Apr 10, 2012. 5:32 AMact casual (author) says:

Yes, i am.

Apr 10, 2012. 11:06 AM

steveastrouk says:

Good. In that case, you can usually get away with the default port settings, but I recommend that you add an external pullup as well. The internal one is pretty weak.

Apr 10, 2012. 5:13 PMact casual (author) says:

how do it

Apr 11, 2012. 12:44 AM

steveastrouk says:

External pull up ? What frequency are you intending to work at ?

Apr 11, 2012. 1:16 AMact casual (author) says:

sorry i read it wrongly
thank you

Apr 9, 2012. 1:59 PM

steveastrouk says:

Ermm. Some of the LPC series have that very functionality - configurably

Apr 9, 2012. 2:08 PM

iceng says:

Didn't know that.......... Really..., open collectors..........

Now I have to apologize to .act casual.

Apr 10, 2012. 2:16 AM

rickharris says:

this might help you

Apr 10, 2012. 5:34 AMact casual (author) says:

I'm not using picaxes I'm using arduino

Apr 10, 2012. 8:38 AM

rickharris says:

Yes I know, BUT the principles are the same - This is a fairly good explanation of what it is all about.

Apr 9, 2012. 12:14 AM

rickharris says:

The pull up resistor is a passive device. In general outputs don't have a pull up they are active pins and will be high low or high impedance.

Can you explain in more detail what your trying to do - Circuit diagrams help.