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PCA9527 working only in one direction Port B -> port A and not the other way around.

Question asked by kartikkaruna on Jun 17, 2016

We have a solution that incorporates a  PCA9527 to extend the I2C bus in order to talk to the sensors on the other end of the line .

However the I2C communication only works in one direction when the master Polls the slave on the far end of the sensor the slave acknowledges the transmission but this ACK never makes it back to the Master and hence the communication fails. Attached is a snippet of the schematic.

also attached is the snippet showing the output of the Logic analyser .

the first two waveforms are on the Port A side of the bus extender ( side that the slave resides , notice that it responds with an ACK)

the next two waves for on the master's side of the PCA9527 (port B side) ( also notice that the ACk never made it across the PCA9527.


Any reason for this to happen ?

any suggestions on where to look ?