I am using an ATMega324PB Xplained board as my I2C master and several custom boards with 324PBs as the slave devices. I also have a MCP23008 which I planned to use to turn on and off the slave devices. However, it appears that when I power down a slave device it causes the entire I2C line to hang. Once I unplug the SDA line (and only the SDA line) of the offending card, the program resumes normal operation.
So my question is, why? I know I had an issue with unprogrammed 324s hanging my line, but I understood that that was because it was powering up the port as a digital input with latched pull-ups. However, I at least assumed that powering off an I2C device would leave the pins floating, as the spec says. Am I just screwed, or am I overlooking something?
Thanks in advance.