I's designing a RaspberryPi "HAT" to fit onto a device which already has the RaspberryPi 7" touchscreen display. That display pretty much leaves the GPIO expansion header free for use apart from the I2C pins used for HAT Identification . Now whilst I2C is can cope with multiple slave devices connected to the BUS the guidelines indicate that the identification EEPROM "I2C address is 0x50". So that means that even though I can add a second HAT only one can use the ID system?
 https://github.com/raspberrypi/hats/blo ... gnguide.md