It is given in philips i2c specification that maximum number of devices connected to the bus is limited by bus capacitance.There is formula specified for pull up resistor but there is no formula to calculate bus capacitance. Then how to calculate bus capacitance?


1 Answer 1


Each device on the I2C bus will contribute to the bus capacitance. These values are taken from the device datasheet and added together. Example taken from the first I2C device datasheet I found, the M24C08:


Remember to include the capacitance of the master device too. Maximum capacitance for the bus is 400pF.

  • 2
    \$\begingroup\$ Don't neglect the capcitance of the cables if the device is remote. \$\endgroup\$ Mar 13, 2013 at 11:05
  • \$\begingroup\$ Is there a way to calculate the capacitance of the cables? I am a bit rusty on the subject but I think it depends on the layout of the connections; if so, is there some way to get an approximate value before hands, or is it something one only measures? \$\endgroup\$
    – user46977
    Jul 8, 2014 at 7:49
  • \$\begingroup\$ Agreed, this computation appears good if the parts are built to specification and you have the datasheet. What can we do if there is no datasheet? Is this something we can measure using an instrument of some kind? \$\endgroup\$ Jun 14, 2016 at 15:09
  • \$\begingroup\$ How to calculate the capacitance contribution of the traces on the PCB? \$\endgroup\$ Sep 18, 2016 at 16:12

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