General Purpose Input

The output buffer is disabled.
The Schmitt trigger input is active.
The pull-up and -down resistors are active, according to PUPDR.
Input data is sampled every AHB clock.
Input data register holds I/O state.

Programming Instructions

Enable Peripheral

Make sure the peripheral is enabled:

Enable GPIOx in RCC→AHBENR[0].

Setup input mode

Configure the MODE and PUPDR register, for every pin that should act as digital input:

Write 0x00 to the corresponding fields in GPIOx→MODE.
Configure pull-up / -down in GPIOx→PUPDR.

Configuration Registers

GPIOx_MODER - GPIO port mode register

Pin x

00

Input mode (reset state)

GPIOx_PUPDR - GPIO port pull-up / pull-down register

Pin x	00	No pull-up, pull-down (reset state)
	01	Pull-up
	10	Pull-down

Data Registers

GPIOx_IDR - Port input data register

* Register is read only