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.

Make sure the peripheral is enabled:

• Enable GPIOx in RCC→AHBENR[0].

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.

GPIO port mode register

GPIO port pull-up / pull-down register

Port input data register

* Register is read only