[TriEmbed] Basic I2C Question

[Jon Wolfe]

You typically have only one set of pull ups on a bus. Sometimes you have to play with the value of the resistors to get better performance.  Using multiple resistors limits your ability to change the effective value. Not only that, but a device with its own pullups is not really "open drain" in that it's not floating/high impedance when high.

When developing, it is convenient to use the builtin pullups on the avr though,  but I put real pullups in the final circuit.

<div>-------- Original message --------</div><div>From: Charles McClelland <chip at mcclellands.org> </div><div>Date:09/11/2014  8:28 AM  (GMT-05:00) </div><div>To: TriEmbed Discussion <triembed at triembed.org> </div><div>Subject: [TriEmbed] Basic I2C Question </div><div>
</div>First, I wanted to thank Paul for the excellent presentation on interrupts.  I now have a Watch Dog Timer routine which is saving me from having to put a clock on one project.  

On my other project though, I still need a clock.  And since I am already using an I2C bus, I thought I could simply add one to that bus.  That way I will have two I2C sensors connected to an Arduino (ATMEGA328).  My question is how to best implement the pull-up the resistors.  Should I put resistors on each (perhaps 10k since they will effectively be in parallel) or should I put one set of pull up resistors on the main board for both?  It seems like the latter is the better approach but I did not know if there was some reason to do one over the other.   

On a related note, I need a 3.3V I2C Real Time Clock with Alarms - I am looking at the DS1339 and hoping I can use some of the DS1307 library since they are both from Maxim.  Any other suggestions?

Thanks,

Chip



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