Given a circuit made of an MCU powered by a laptop's USB port (such as tm4c123gh6pm), and an external power supply, should the MCU's GND pin be wired to the external power supply negative terminal?
For instance, in a circuit made of the above MCU exposing an I2C master and a slave, with two external pull-up resistors powered by a 3.3V buck converter, which in turn is powered by a 9V battery. Should the 9V battery negative terminal be connected to one of the MCU GND pins?