AN4228 datasheet(43/90 Pages) STMICROELECTRONICS

43 / 90 page

DocID024110 Rev 5

43/90

AN4228

Firmware migration using the library

has a multiplexer with sixteen alternate function inputs (AF0 to AF15) that can be configured

through the GPIO_PinAFConfig () function:



After reset, all I/Os are connected to the system’s alternate function 0 (AF0)



The peripherals’ alternate functions are mapped by configuring AF0 to AF15.

In addition to this flexible I/O multiplexing architecture, each peripheral has alternate

functions mapped onto different I/O pins to optimize the number of peripheral I/O functions

for different device packages; for example, the USART2_RX pin can be mapped on PA3 or

PA15 pin.

The configuration procedure is the following:

Connect the pin to the desired peripherals' Alternate Function (AF) using

GPIO_PinAFConfig() function

Use GPIO_Init() function to configure the I/O pin:

Configure the desired pin in alternate function mode using



GPIO_InitStructure->GPIO_Mode = GPIO_Mode_AF;

Select the type, pull-up/pull-down and output speed via



GPIO_PuPd, GPIO_OType and GPIO_Speed members

The example below shows how to remap USART2 Tx/Rx I/Os on PD5/PD6 pins in

STM32F1 series:

/* Enable APB2 interface clock for GPIOD and AFIO (AFIO peripheral is used

to configure the I/Os software remapping) */

_APB2PeriphClockCmd(_APB2Periph_GPIOD | _APB2Periph_AFIO, ENABLE);

/* Enable USART2 I/Os software remapping [(USART2_Tx,USART2_Rx):(PD5,PD6)]

GPIO_PinRemapConfig(GPIO_Remap_USART2, ENABLE);

/* Configure USART2_Tx as alternate function push-pull */

GPIO_InitStructure.GPIO_Pin = GPIO_Pin_5;

GPIO_InitStructure.GPIO_Mode = GPIO_Mode_AF_PP;

GPIO_InitStructure.GPIO_Speed = GPIO_Speed_50MHz;

GPIO_Init(GPIOD, &GPIO_InitStructure);

/* Configure USART2_Rx as input floating */

GPIO_InitStructure.GPIO_Pin = GPIO_Pin_6;

GPIO_InitStructure.GPIO_Mode = GPIO_Mode_IN_FLOATING;

GPIO_Init(GPIOD, &GPIO_InitStructure);

In STM32F3 series, update this code as follows:

/* Enable GPIOA's AHB interface clock */

_AHBPeriphClockCmd(_AHBPeriph_GPIOA, ENABLE);

/* Select USART2 I/Os mapping on PA14/15 pins

[(USART2_TX,USART2_RX):(PA.14,PA.15)] */

/* Connect PA14 to USART2_Tx */

GPIO_PinAFConfig(GPIOA, GPIO_PinSource14, GPIO_AF_2);

/* Connect PA15 to USART2_Rx*/

GPIO_PinAFConfig(GPIOA, GPIO_PinSource15, GPIO_AF_2);

/* Configure USART2_Tx and USART2_Rx as alternate function */

GPIO_InitStructure.GPIO_Pin = GPIO_Pin_14 | GPIO_Pin_15;

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