IO mode in STM32

Select IO mode in STM32
(1) Floating input_IN_FLOATING - floating input, can be used for KEY identification, RX1
(2) Pull-up input_IPU - IO internal pull-up resistor input
(3) Pull-down input_IPD - IO internal pull-down resistor input
(4) Analog input_AIN - use ADC analog input, or save power under low power consumption
(5) Open drain output_OUT_OD - IO output 0 is connected to GND, IO output 1, floating, an external pull-up resistor is required to achieve high output level. When the output is 1, the state of the IO port is pulled high by the pull-up resistor, but because it is an open drain output mode, the IO port can also be changed to a low level or unchanged by an external circuit. The IO input level change can be read to realize the IO bidirectional function of C51
(6) Push-pull output _OUT_PP - IO output 0- connected to GND, IO output 1 - connected to VCC, the read input value is unknown
(7) Multiplexed function push-pull output _AF_PP - on-chip peripheral function (SCL, SDA of I2C)
(8) Multiplexed function open-drain output _AF_OD - on-chip peripheral function (TX1, MOSI, MISO.SCK.SS)
STM32 setting example:
(1) Simulate I2C using open-drain output _OUT_OD, connected to a pull-up resistor, and can correctly output 0 and 1; when reading the value, first GPIO_SetBits(GPIOB, GPIO_Pin_0); pull high, and then you can read the IO value; use GPIO_ReadInputDataBit(GPIOB, GPIO_Pin_0);
(2) If there is no pull-up resistor, the IO is high by default; if you need to read the value of the IO, you can use the pull-up input_IPU, floating input_IN_FLOATING and open-drain output_OUT_OD