GPIO 8 Common Modes

GPIO (General Purpose Input/Output) is used to interface with external circuits. On STM32/PY32, common modes include:

• floating input
• pull-up input
• pull-down input
• analog input
• push-pull output
• open-drain output
• alternate-function push-pull
• alternate-function open-drain

Input Modes

Floating input (GPIO_Mode_IN_FLOATING)

The pin is high-impedance and not internally pulled up/down. External circuitry determines level.

1
2
3
4

GPIO_InitStruct.Pin = GPIO_PIN_0;
GPIO_InitStruct.Mode = GPIO_MODE_INPUT;
GPIO_InitStruct.Pull = GPIO_NOPULL;
HAL_GPIO_Init(GPIOA, &GPIO_InitStruct);

Pull-up input (GPIO_Mode_IPU)

Internal pull-up resistor keeps default level high.

Pull-down input (GPIO_Mode_IPD)

Internal pull-down resistor keeps default level low.

Output Modes

Push-pull output

Can actively drive both high and low levels. Good for general digital output.

Open-drain output

Can actively pull low; high level typically provided by pull-up resistor. Useful for shared bus (for example I2C-like signaling).

Analog Mode

Analog mode disconnects digital input/output path and is used for ADC/analog signals.

Practical Selection Tips

• Button input: pull-up or pull-down.
• LED/general control pin: push-pull output.
• Wired-AND/shared line: open-drain + pull-up.
• ADC pin: analog mode.