General-purpose I/Os (GPIO) RM0091
118/742 Doc ID 018940 Rev 1
8 General-purpose I/Os (GPIO)
8.1 GPIO introduction
Each general-purpose I/O port has four 32-bit configuration registers (GPIOx_MODER,
GPIOx_OTYPER, GPIOx_OSPEEDR and GPIOx_PUPDR), two 32-bit data registers
(GPIOx_IDR and GPIOx_ODR), a 32-bit set/reset register (GPIOx_BSRR), a 32-bit locking
register (GPIOx_LCKR) and two 32-bit alternate function selection registers (GPIOx_AFRH
and GPIOx_AFRL).
8.2 GPIO main features
● Output states: push-pull or open drain + pull-up/down
● Output data from output data register (GPIOx_ODR) or peripheral (alternate function
output)
● Speed selection for each I/O
● Input states: floating, pull-up/down, analog
● Input data to input data register (GPIOx_IDR) or peripheral (alternate function input)
● Bit set and reset register (GPIOx_BSRR) for bitwise write access to GPIOx_ODR
● Locking mechanism (GPIOx_LCKR) provided to freeze the port A or B I/O configuration
● Analog function
● Alternate function selection registers for ports A and B (at most 16 AFs possible per
I/O)
● Fast toggle capable of changing every two clock cycles
● Highly flexible pin multiplexing allows the use of I/O pins as GPIOs or as one of several
peripheral functions
8.3 GPIO functional description
Subject to the specific hardware characteristics of each I/O port listed in the datasheet, each
port bit of the general-purpose I/O (GPIO) ports can be individually configured by software
in several modes:
● Input floating
● Input pull-up
● Input-pull-down
● Analog
● Output open-drain with pull-up or pull-down capability
● Output push-pull with pull-up or pull-down capability
● Alternate function push-pull with pull-up or pull-down capability
● Alternate function open-drain with pull-up or pull-down capability
Each I/O port bit is freely programmable, however the I/O port registers have to be accessed
as 32-bit words, half-words or bytes. The purpose of the GPIOx_BSRR register is to allow
atomic read/modify accesses to any of the GPIO registers. In this way, there is no risk of an
IRQ occurring between the read and the modify access.
To Next Page
Loading...
Need help?
General
