General-Purpose And Alternate-Function I/Os (Gpios And Afios); Gpio Functional Description - ST STM32F102 Series Reference Manual

RM0008
7 General-purpose and alternate-function I/Os (GPIOs
and AFIOs)
Low-density devices are STM32F101xx, STM32F102xx and STM32F103xx
microcontrollers where the Flash memory density ranges between 16 and 32 Kbytes.
Medium-density devices are STM32F101xx, STM32F102xx and STM32F103xx
microcontrollers where the Flash memory density ranges between 64 and 128 Kbytes.
High-density devices are STM32F101xx and STM32F103xx microcontrollers where the
Flash memory density ranges between 256 and 512 Kbytes.
This Section applies to the whole STM32F10xxx family, unless otherwise specified.
7.1

GPIO functional description

Each of the general-purpose I/O ports has two 32-bit configuration registers (GPIOx_CRL,
GPIOx_CRH), two 32-bit data registers (GPIOx_IDR, GPIOx_ODR), a 32-bit set/reset
register (GPIOx_BSRR), a 16-bit reset register (GPIOx_BRR) and a 32-bit locking register
(GPIOx_LCKR).
Subject to the specific hardware characteristics of each I/O port listed in the datasheet, each
port bit of the General Purpose IO (GPIO) Ports, can be individually configured by software
in several modes:
●
Input floating
●
Input pull-up
●
Input-pull-down
●
Analog Input
●
Output open-drain
● Output push-pull
●
Alternate function push-pull
● Alternate function open-drain
Each I/O port bit is freely programmable, however the I/O port registers have to be accessed
as 32-bit words (half-word or byte accesses are not allowed). The purpose of the
GPIOx_BSRR and GPIOx_BRR registers is to allow atomic read/modify accesses to any of
the GPIO registers. This way, there is no risk that an IRQ occurs between the read and the
modify access.
Figure 10

General-purpose and alternate-function I/Os (GPIOs and AFIOs)

shows the basic structure of an I/O Port bit.
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