i2c + one-wire (draft)

I2C + one-wire - Community Recommended Pinout DRAFT 4th Feb 2015

This is a page for the community recommended i2c pinouts. Currently in draft status, thus is up for discussion still.

modular plug

8PxC connectors


    8P8C (wired as twisted pair Cat5 ) I2C Plug PORT:
    (You can use standard straight through RJ45 Ethernet cable) 

                      _____
                    _|     |_
     ______________|         |_______________
    |                                        |
    |                                        |
    |                                        |
    |[OWD][GND][SCL][SCL][GND][GND][AUX][INT]|
       ^    ^   ^    ^    ^    ^    ^     ^
       8    7   6    5    4    3    2     1

     Pin (i2c) :
      * 8 : OWD
      * 7 : GND
      * 6 : SDA
      * 5 : SCL
      * 4 : GND (Twisted with pin 5 in cat5 cable)
      * 3 : GND (Twisted with pin 6 in cat5 cable)
      * 2 : AUX Unregulated (Typically Max 12V)
      * 1 : Interrupt from slaves to master

Justification/Reasoning

Swapping the dedicated 5V and 3.3V rail for i2c for a twisted pair of i2c devices.

This means you will need a voltage regulator for every node.

OWD is twisted with it's own ground. Same goes with i2c pins. This minimises wiring crosstalk.

6PxC connectors

This is essentially a compact version of the 8P8C scheme above.


    6P6C PORT (Telephone. Typically called RJ12):
    (6 Possible Contacts, 4 Pin Contacts Used)
            _____
          _|     |_
     ____|         |____
    |                   |
    |                   |
    |                   |
    |_   6 5 4 3 2 1   _|

     Pin (i2c) :
      * 6 : OWD - One Wire
      * 4 : SDA
      * 3 : GND
      * 2 : SCL
      * 5 : AUX Unregulated (Typically Max 12V)
      * 1 : Interrupt from slaves to master 

    http://en.wikipedia.org/wiki/Registered_jack#Registered_jack_types

Justification/Reasoning

Swapping dedicated common voltage rail in the i2c only version, for the One wire connection.

This means you will need a voltage regulator for every node.

However OWD's proximity to SDA i2c data pin, may potentially have crosstalk as a problem.

If this worries you enough. Then you can try the combo cat5 port scheme in this page above (8PxC connectors).

Questions to all

Should we just remove the modular version for single mode operation of either i2c or one-wire in the other pages? You lose the dedicated voltage rails, thus you need individual regulator for every one.

But on the other hand by keeping to one standard for both one-wire and i2c devices, it will make wiring easier.

I personally think that at the very least we should make the "cat5 RJ45 8PxC" version common to both, while keeping the telephone wire method custom. This is since the compact form for the telephone version in this page runs the risk of crosstalk between one-wire and i2c pins in longer runs.

Also the shared interrupts would be shared by both one wire and i2c devices.