i use philips pcf8574 and dallas ds1621 chips on the bus. remember that the resistive load is really low (i use 4k7 pullups, only one on each wire). what you get is high capacitive load. with the serial resistors, you reduce the switching current to below 10ma. the 3ma specified is the minimum constant current, a deivce is able to provide! (absolute max for pcf8574 is 25ma) a system with about 24 nodes works well now for more than 1.5 years without any problems. tino Olin Lathrop Gesendet von: pic microcontroller discussion list 28.02.02 13:53 Bitte antworten an pic microcontroller discussion list An: PICLIST@MITVMA.MIT.EDU Kopie: Thema: Re: [PIC]: I2C Questions > i have a star topology with serial resistors > (about600..800 ohms) in the scl and sda wires at each node. > that works fine! Don't try this at home, folks. A number of standard IIC devices may not work this way, or may even get damaged. The IIC bus is specified with a maximum sink current of 3mA on each line. If you're going to recommend something like this, please point out that you are only using IIC protocol, not true IIC. I assume you are using your own line drivers and not connecting off the shelf IIC devices to the bus, right? ******************************************************************** Olin Lathrop, embedded systems consultant in Littleton Massachusetts (978) 742-9014, olin@embedinc.com, http://www.embedinc.com -- http://www.piclist.com hint: The PICList is archived three different ways. See http://www.piclist.com/#archives for details. -- http://www.piclist.com hint: The PICList is archived three different ways. See http://www.piclist.com/#archives for details.