<html><head><meta http-equiv="Content-Type" content="text/html; charset=UTF-8"></head><body >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.<div><br></div><div>When developing, it is convenient to use the builtin pullups on the avr though, but I put real pullups in the final circuit.</div><br><br><div>-------- Original message --------</div><div>From: Charles McClelland <chip@mcclellands.org> </div><div>Date:09/11/2014 8:28 AM (GMT-05:00) </div><div>To: TriEmbed Discussion <triembed@triembed.org> </div><div>Subject: [TriEmbed] Basic I2C Question </div><div><br></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. <br><br>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. <br><br>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?<br><br>Thanks,<br><br>Chip<br><br><br><br>_______________________________________________<br>Triangle, NC Embedded Computing mailing list<br>TriEmbed@triembed.org<br>http://mail.triembed.org/mailman/listinfo/triembed_triembed.org<br>TriEmbed web site: http://TriEmbed.org<br></body>