My question concerns the ability to connect multiple port B's of two different PCA9617A devices to the same bus.
I my application I have a single master device (an LPC1769 MCU) that must communicate with two slaves. The slaves need to communicate back to the master; however, they do not need to communicate with each other.
It is recommended by the datasheet that in a star configuration such as this the master be connected to the port A sides and the two slaves be connected to the port B side. However, in my application, the slaves connected to the B side are connected to a moderately long cable (~0.5m) and have an Output Low Level Voltage that is 0.4V max. I am concerned that in some marginal cases, a slave may not be able to pull the voltage below the 0.4V the port B side needs to trigger a low output.
This would be resolved by using the port A side with the slave; however, this would then require two port B sides to be connected to the single master.
What are all the concerns with having multiple port B sides connected to the same bus? It seems to me there is only one reason why you wouldn't want to do this: the port B output of one PCA9617A can only bring the I2C bus voltage down to 0.54V - 0.6V which would not register as a low voltage to the other PCA9617A.
However, in my application, I do not need the slaves to be able to communicate with each other and therefore, I do not care if the low from one PCA9617A does not register. The 0.54V - 0.6V low voltage will still register with the MCU as a low and the MCU will still be able to send data through to the slaves.
Are there any other problems that could occur if two port B sides are connected? Otherwise it seems like I would be fine to do this.