LayerscapeのトピックRe: I2C Slave detect Repeated Start

I2C Slave detect Repeated Start

gauthamkrishnan_r — Fri, 26 Feb 2021 09:56:07 GMT

If a Master I2C device is communicating with a Slave I2C device and generates a Repeated Start condition and starts communicating with second Slave I2C device, how will the first Slave device detect the Repeated Start condition? Will it be able to detect the Repeated Start at all, or will it keep waiting until the Master addresses it again?

Re: I2C Slave detect Repeated Start

r8070z — Mon, 01 Mar 2021 05:54:05 GMT

The I2C specs says:

I2C-bus compatible devices must reset their bus logic on receipt of a START or repeated START condition such that they all anticipate the sending of a slave address, even if these START conditions are not positioned according to the proper format.

Re: I2C Slave detect Repeated Start

gauthamkrishnan_r — Mon, 01 Mar 2021 06:48:48 GMT

Does it mean my slave device will not be able to recognize that the Master has started communicating to another slave device using a Repeated Start?

Re: I2C Slave detect Repeated Start

r8070z — Mon, 01 Mar 2021 07:42:36 GMT

It means that a START condition and repeated START condition treated in the same way and the slave address will be checked.

Re: I2C Slave detect Repeated Start

gauthamkrishnan_r — Mon, 01 Mar 2021 09:26:57 GMT

Agree, but what will be the effect of the Repeated Start on the first slave device once the Master starts communicating with second slave device? The communication with first slave device is not cleanly terminated.

Re: I2C Slave detect Repeated Start

r8070z — Fri, 05 Mar 2021 03:36:12 GMT

What do you mean as communication with first slave device is clearly terminated? How it should be done?

Re: I2C Slave detect Repeated Start

gauthamkrishnan_r — Fri, 05 Mar 2021 04:40:21 GMT

I mean a 'clean termination' is done by a Stop condition, but in the absence of a Stop condition to the first slave device (when master initiates a Repeated Start followed by slave address of another slave device), the first slave device will not be able to recognize that master's communication with it has ended.

Re: I2C Slave detect Repeated Start

danielholala — Wed, 09 Feb 2022 08:57:23 GMT

I clearly understand the situation you are describing.

I'd hope that the first slave device would ignore the transaction with the second slave device (that's what I2C addresses are for, right) and thus keep its internal state machine (unaffected by the transaction with the second slave). But I don't know for sure whether I2C supports these kind of "piecewise" transactions.

Therefore I wonder why there's no reply from NXP. I'd be happy to have an official view on this situation.