March 2015

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AN4457

Application note

Implementing an emulated universal asynchronous receiver

transmitter on STM32F4 microcontroller series

Introduction

This application note describes how to implement an emulated universal asynchronous

receiver transmitter (UART) on STM32F4 series.

Such an emulator is needed in applications that require more UARTs than the ones provided

by STM32F4 microcontrollers.

The emulated UART is full-duplex, supports up to 9 data bits and baud rates up to

115200 bps. It also offers a high flexibility since any I/O pin can be used as TX or RX line. In

addition, this UART emulation uses the DMA to minimize CPU usage.

This application note provides a basic example of communications between a hardware and

a software UART as well as a summary of CPU load and firmware footprint.

The STSW-STM32156 firmware package is delivered with this document and contains the

source code of the UART emulator with all firmware modules required to run the example.

Table 1. Applicable products

Type

Part numbers

Microcontrollers

STM32F4 series

Embedded software

STSW-STM32156

www.st.com