AN4088 datasheet(29/71 Pages) STMICROELECTRONICS

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AN4088

Peripheral migration

Alternate function mode

In 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).

In STM32F0 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).

The I/O pins are connected to on-chip peripherals/modules through a multiplexer that

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

this way, there can be no conflict between peripherals sharing the same I/O pin. Each

Table 16. GPIO differences between STM32F1 series and STM32F0 series

GPIO

STM32F1 series

STM32F0 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

10 MHz

48 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

18 MHz

12 MHz

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