AN4228 datasheet(27/90 Pages) STMICROELECTRONICS

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DocID024110 Rev 5

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AN4228

Peripheral migration

written for the STM32F1 series using the GPIO needs to be rewritten to run on STM32F3

series.

For more information about STM32F3 GPIO programming and usage, please refer to the

“I/O pin multiplexer and mapping” section in the GPIO chapter of the STM32F3xx reference

manuals (RM0313 and RM0316).

The table below presents the differences between GPIOs in the STM32F1 series and

STM32F3 series.

3.7.1

Alternate function mode

STM32F1 series

The configuration to use an I/O as an alternate function depends on the peripheral mode

used. For example, the USART Tx pin should be configured as an alternate function push-

pull, while the USART Rx pin should be configured as input floating or input pull-up.

To optimize the number of peripheral I/O functions for different device packages (especially

those with a low pin count), it is possible to remap some alternate functions to other pins by

software. For example, the USART2_RX pin can be mapped on PA3 (default remap) or PD6

(by software remap).

STM32F3 series

Whatever the peripheral mode used, the I/O must be configured as an alternate function,

then the system can use the I/O in the proper way (input or output).

Table 14. GPIO differences between STM32F1 and STM32F3 series

GPIO

STM32F1 series

STM32F3 series

General

purpose

output

PP + PU

PP + PD

OD + PU

OD + PD

Alternate

function

output

PP + PU

PP + PD

OD + PU

OD + PD

Alternate

function

selection

To optimize the number of peripheral I/O

functions for different device packages, it

is possible to remap some alternate

functions to some other pins (software

remap).

Highly flexible pin multiplexing allows no

conflict between peripherals sharing the

same I/O pin.

Max IO

toggle

frequency

18 MHz

36 MHz

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