AN3427 datasheet(30/52 Pages) STMICROELECTRONICS

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Peripheral migration

AN3427

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Doc ID 019001 Rev 1

3.6.1

Alternate function mode

In STM32 F1 series

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

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

pull while 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 with those with low pin count), it is possible by software to remap some

alternate functions to other pins. For example, the USART2_RX pin can be mapped on

PA3 (default remap) or PD6 (done through software remap) pin.

In STM32 F2 series

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

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

The I/O pins are connected to onboard peripherals/modules through a multiplexer that

allows only one peripheral’s alternate function to be connected to an I/O pin at a time.

Table 9.

GPIO differences between STM32 F1 series and STM32 F2 series

GPIO

STM32 F1 series

STM32 F2 series

Input mode

Floating

General purpose

output

PP + PU

PP + PD

OD + PU

OD + PD

Alternate Function

output

PP + PU

PP + PD

OD + PU

OD + PD

Input / Output

Analog

Output speed

2 MHz

10 MHz

50 MHz

2 MHz

25 MHz

50 MHz

100 MHz

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 16 MHz

60 MHz

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