The maximum input voltage at all IO ports (including peak signal current) cannot exceed 3.1 V
because the module uses a 2.8 V IO power system. In the application of the module, the IO output
voltage from the 3.3 V power supply system of the external circuit might greatly overshoot 3.1 V due to
the signal integrity design. In this situation, the IO pins of the module might be damaged if the IO signals
are connected to the IO port on the 2.8 V systems. To rectify this issue, take measures to match the
level. For details, see the 3.2 UART.