I have 2 Uno R3 boards talking back and forth to each other via I2C (simple messages). All is well. No problems. When I pull power on either board (to simulate a fault in the wire, dead battery, failed board, etc) the other board hangs at the wire.endTransmission() point. This is the exact spot it hangs. I can;t even get a return code: just freezes. If I power up the "broken" board and chatter returns to normal like nothing happened.
chucktodd: Thank you. I am going to look into the PCA9545A. Thank you for explaining to me what the darn thing is and what the issues are... :-)
One more question: with the comments I rem in / out make it compatable with the current Arduino environment (1.8x)?