Instructables

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


You don't set the pull up/downs in the output mode on an AVR, you can only do it for input mode.
+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
act casual (author)  iceng2 years ago
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You're using the onboard TWI aren't you ?
act casual (author)  steveastrouk2 years ago
Yes, i am.
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.
act casual (author)  steveastrouk2 years ago
how do it
External pull up ? What frequency are you intending to work at ?
act casual (author)  steveastrouk2 years ago
sorry i read it wrongly
thank you
Ermm. Some of the LPC series have that very functionality - configurably
Didn't know that.......... Really...,  open collectors..........

Now I have to apologize to .act casual.
rickharris2 years ago
this might help you
act casual (author)  rickharris2 years ago
I'm not using picaxes I'm using arduino
Yes I know, BUT the principles are the same - This is a fairly good explanation of what it is all about.
rickharris2 years ago
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.