Pios (80 in total) are distributed in 5 ports, each of which has 16 GPIOs. The 16 GPIOs are named with names from A to E. The maximum voltage is 5V. Most of the external pins can be switched from a general-purpose GPIO to a dedicated I\/O port for the user device.
The STM32 also has an external interrupt control unit that allows 16 GPIOs on each port to be mapped to an external interrupt input.