 The number of nodes which can exist on a given I2C bus is limited by the address space and also by the total bus capacitance of 400 pF, which restricts practical communication distances to a few meters.The relatively high impedance and low noise immunity requires a common ground potential, which again restricts practical use to communication within the same PC board or small system of boards.The aforementioned reference design is a bus with a clock (SCL) and data (SDA) lines with 7-bit addressing.