I2C pull-up Resistor Calculation

Hi @amphitryonoff,

  Short answers ...

• Are there programs to compute the required resistors value?     
  • No! 
• How may I determine the 'Bus Capacitance' of my circuitry?    
  • You don't. Build circuit and check I2C waveforms

 I2C was invented by Philips, as a cheap way of networking chips within a Colour TV. They effectively 'Open Sourced' the system, albeit it was patented, and chip manufacturers may have paid license fees to include I2C pins on their chips.Equipment using such chips do not need to pay extra fees.

Part of that 'Open Sourcing' included a widely distributed Application Note, dated approximately 1992, and my above answer is my summary recall of that note.

A more recent (2003) discussion at https://www.nxp.com/docs/en/application-note/AN10216.pdf may provide some further insight.

Best wishes, Dave

Hi @davee !

Posted by: @davee

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A more recent (2003) discussion at https://www.nxp.com/docs/en/application-note/AN10216.pdf /a> may provide some further insight.

TY for this reference. Slide 32 on p. 13 shows for the pullup resistors "Typical value 2 kΩ to 10 kΩ", but that is vs a Vcc of 5V. When I calculate as suggested in "I2C pull-up Resistor Calculation" I get (for Standard Mode) a range from 967 Ω to 2.95 kΩ -- what is at least in the same magnitude but 1:3 apart. My uneducated choice is 2k6, but with the shaky self-confidence of an apprentice chef preparing his first menu for a client in absence of his master.

Posted by: @amphitryonoff

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Slide 32

Nope -- slide 31.