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I am wondering are there any standards for the order of signals on I2C header? We get many I2C devices on the market, but the order of pins on the headers is inconsistent and hence we may not be able to insert any I2C device to our board. For example, some devices have VCC GND SCL SDA, some of them have GND VCC SDA SCL and like this there are many combinations. I understand that I2C is typically used within the board itself and hence order may not be defined. But the order of pins would matter for external devices that may be soldered directly to the header.

Rajesh
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I am wondering are there any standards for the order of signals on I2C header? [...] I understand that I2C is typically used within the board itself and hence order may not be defined.

The order of pins on any I2C connector is not defined in the I2C specification. Therefore any connector used for I2C, and the order of signals on that connector, are chosen for other reasons.

The I2C specification does recommend a PCB or ribbon cable "wiring pattern" as follows - this does not specify pin order on a connector, but is relevant:

I2C specification section 7.5 - Wiring pattern of the bus lines

(Image source: I2C specification section 7.5 - Wiring pattern of the bus lines)

Some companies have made their own standard connector pinout for I2C e.g. Seeed / Seeedstudio Grove I2C devices. However any connector / pinout standardisation cannot be relied upon for other products, which don't claim to meet that company-specific "standard".

These previous questions also discuss I2C signal order on connectors:

SamGibson
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There is no standard connector, except for interfaces that add something of their own to just use I2C protocol and electrical standards. If you look at I2C standard there is a suggestion how to wire them. If I recall, power supplies were two pins at the center, and SDA and SCL were the two edge pins. This is to have tight coupling between power wires and to have least crosstalk between SDA and SCL pins.

Justme
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  • If power supply pins are at the center, accidental reverse connection protection is not available (unless it is provided inside the I2C device). – Rajesh Nov 04 '19 at 15:43
  • @Rajesh Whatever the order of the signals you choose, there is a way to screw the board or device up by randomly exchanging them. If you need reverse connection protection, implement a dedicated machanism for that (it could be mechanical, or electronic with some additional circuitry). Don't expect the chips to withstand *any* kind of miswiring. To make it clear: exchanging VCC and GND will surely burn the chip. But exchanging VCC and SCL will likely kill it too, because at some point, there will be a short through the protection diodes. – dim Nov 04 '19 at 15:51
  • Well make your own connector with more pins. Put supply to center and then grounds on both sides. Wrong orientation will not fry the board then. – Justme Nov 04 '19 at 16:41