Hi, Be aware the value of the pull-up resistors (in combination with the overall capacitance of the connected devices) defines the rise and fall times of the signals on the IIC communication bus. And these rise and fall times are in direct relation with the maximum communication speed possible.
In short: the lower the bus capacitance and pull-up resitor value, the faster the communication speed allowed on the bus. BUT, there is a limit: be aware of the specification about maximum allowed sink-current of each single device . Kind regards, Nico ----- Original Message ----- From: Geert Vancompernolle To: [email protected] Sent: Thursday, April 05, 2007 7:42 PM Subject: [foxboard] Re: Coming back to PCF8591 --- In [email protected], "rieupinfor" <[EMAIL PROTECTED]> wrote: > > Hi Geert, > Do you put resistors on the SDA and SCL on each i2c circuit on the > bus, or only one pair on the "fox side ?" > Thanks > Best regards > Hi, It's indeed only one pair of resistors that should be used. Only one device at a time can "communicate" with the master, so only one device at a time will "pull" on the SDA line. That's one. Second, if you would put those resistor pairs on every device, they would be put in parallel one with the other: all pull-up resistors on the SDA line would be put in parallel, same for all pull-up resistors on the SCL line. In the end, almost no resistance would be left over (in the limit, you would nearly short circuit the SDA and SCL lines with the +Vcc line...). And that would not be your intention, wouldn't it? ;-) Best rgds, --Geert [Non-text portions of this message have been removed]
