March 2015

DocID027483 Rev 1

1/21

1

AN4655

Application note

Virtually increasing the number of serial communication peripherals

in STM32 applications

Introduction

Application engineers often face the problem of limited number of serial communication

peripherals of a microcontroller that, on the other hand fulfills all the other application

requirements thanks to its features and performance. Sometimes they obviate by switching

to a higher level microcontroller with sufficient number of communication peripherals. This

migration brings with it additional (often unused) performance and functionality, in most

cases unneeded and not used by application, in addition to increased costs and PCB

complexity.

A frequent case is when full (or specific) functionality is not required for each and every

channel, in this case the communication flow and its control can be simplified radically (e.g.

communication is required at specific modes or time slots only, communication speed can

be lower, correct timing is not strictly required for all the signals, simplified protocol or flow is

acceptable). In these specific cases the user would really benefit from methods on how to

supplement the missing channel(s) with current HW, to avoid needless migrations.

On the other side, reaching nearly full compatibility with all the native HW features is hardly

achievable at an alternate channel, besides costing a lot in terms of code and performance.

Usually it is preferable to abandon some specific requirements with the goal of simplify the

concept of the alternated peripheral channel. A crucial point here is to recognize those

undemanding channels in the application, which can be altered with lower effort and loss of

performance.

This application note provides a basic overview of the described issue, and will help the

application engineers to identify possible alternate methods when implementing missing

communication channels. It applies to all STM32 microcontrollers, as the discussed

peripherals are present on all products of this class.

Additional informations and examples can be found in the following reference documents,

describing actual cases and solutions:

• TN0072, Software toolchains and STM32 features;

• UM0892, STM32 ST-LINK Utility software description;

• AN4457, STM32F4 full Duplex UART emulation.

The last cited document is being developed together with other application notes on the

www.st.com