Switch a differential I²C bus section, controlled via I²C

by Peter   Last Updated July 23, 2018 15:25 PM

I want to separate a section of an I²C bus, controlled via an I²C message. (Similar to an I²C bus switch/multiplexer like e.g. PCA9540.)

Indeed the I²C bus to switch isn't a plain vanilla I²C bus, but rather a 4 wire differential bus. I wanted to save myself from converting to and from plain I²C before and after a PCA9540, so I got the idea to use a quad SPDT (rather a 4PDT) to select between connection and separation (with termination) (e.g. (74)CBT3257).

Problem: Usual I²C-IOs update their IOs during the acknowledge phase, but not after stop condition. So controlling the 4PDT by some of them leads to bus separation while SDA and SCL are both low, ending up in a race condition of both separated I²C lines pulled up simultaneously.

Does anybody know of an I²C-IO with IO-update delayed until stop condition? Is there a simple possibility to use a I²C multiplexer (which usually are delayed until stop condition, of course) to control the 4PDT? Any other ideas?

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