Under Development: Microcontrollers

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Newer, faster, better

As technology progresses, newer, faster, and better microcontrollers become available, and therefore the dev team works in the background on porting and testing of DCC-EX on newer generations of microcontrollers to see if they might better suit the DCC-EX project.

This is never done lightly, as the effort to support a new microcontroller might be high and the benefits may be too inconsequential, or indeed may mean loss of functionality.

Considerations for new microcontrollers

When considering new microcontrollers to test and experiment with as potential candidates for EX‑CommandStation, these are the sorts of concerns taken into account (there are more considerations than this of course, these are just the highlights):

  • Architecture/code portability - how much work is required to adapt the codebase to support the architecture?

  • Form factor - can existing users use their existing motor shields and accessories with them?

  • Availability - with continuing microchip shortages impacting supply, is it still generally and easily available in quantity, and globally as we have users all over the world?

  • Sustainability - is the manufacturer deprecating the series or likely to?

  • Price - is it available at a price point that would encourage users to adopt it readily?

  • Quality - is it available with a sufficient build quality to make it reliable?

Notes on 3v3 vs. 5V microcontrollers

It’s important to note that the newer generations of microcontrollers almost always operate at 3.3 volts rather than 5 volts.

For some, like the STM32F4xx range, this is a non-issue as their digital I/O pins are designed to be 5V tolerant, meaning your existing sensors, serial devices, and I2C devices running at 5V are expected to be compatible. Outputs may need further consideration though, as while a “high” signal at 3v3 will trigger most 5V input logic devices, in some rare instances it can potentially not provide a high enough voltage. Using level shifters for digital outputs will resolve these issues, and if you want an extra layer of caution, you can use level shifters for the digital inputs as well.

For others that are not 5V tolerant, using 5V accessories will cause damage to the microcontroller, so using digital I/O level shifters is mandatory with these.

ALL 3v3 microcontrollers require analog inputs to be restricted to no more than 3.3V. This means only some Motor Driver boards are compatible unmodified with 3v3 microcontrollers to read output current. For the moment we recommend the genuine Ardiuno Motor Driver R3, and only the R3 version of it. Motor Drivers such as the Deek Robot can be modified readily enough. We will document this, but in the meantime ask on the Discord server.


Some devices such as the ESP01 WiFi board and HC05/06 Bluetooth boards are already 3v3 devices, so if you have set these up with level shifters, the level shifters will no longer be required when using 3v3 microcontrollers.

STMicroelectronics STM32 NUCLEO series

STMicroelectronics has a range of ARM based microcontrollers that are generally available, sold from reputable global resellers such as Digi-Key and Mouser, and have exceptional build quality for their price (often lower than clone Arduino models!)

Further to this, the NUCLEO series of development boards also provide Arduino Uno compatible header sockets, meaning existing motor (and other) shields can just plug straight in, providing they are 3v3 compatible (see note above).

All of the NUCLEO series being considered as a future DCC-EX platform have a great deal more RAM (128KB to 256KB vs 8KB for a Mega), double or more FLASH (512KB to 2MB) for program storage, and much faster CPU speed (100 to 180Mhz vs 16Mhz) than the current AVR-based UNO and Mega.

With those attributes comes the potential to support much larger EX-RAIL scripts, more Withrottle connections, and many new features.


The majority of the current development work with the Nucleo series has been focused on the NUCLEO-F411RE as it most closely resembles the ubiquitous Arduino Uno form factor, including having Uno compatible header sockets in addition to Morpho pins for a much larger I/O capability than an Uno.

The F411RE has 50 I/O pins compared with the Uno’s 20, and only 20 less than the Arduino Mega despite its diminuitive size. For most use cases it is therefore a suitable substitute for a Mega.

There are larger NUCLEO footprints available (see below), which have many more pins than an Arduino Mega.

A good summary if the F411RE is available on the arm MBED Nucleo-F411RE page.

The NUCLEO-F446RE is the same Nucleo-64 size as the F411RE, but with a faster processor and other features. As one of our more advanced early alpha test users has this board, it’s now also supported as a build target for DCC-EX and being actively tested.

A good summary if the F446RE is available on the arm MBED Nucleo-F446RE page.

Both the F411RE and F446RE are supported in the Arduino IDE.


These are three of the larger NUCLEO devices being tested in the Nucleo-144 form factor; the NUCLEO-F412ZG, NUCLEO-F446ZE and NUCLEO-F429ZI.

Each of these has a larger footprint than the Nucleo-64 series, while still retaining the Uno compatible header sockets, with 114 I/O pins. That said, they are only slightly larger (20mm wider, 33mm longer) than an Arduino Mega 2560.

The F412ZG is potentially suitable as a larger replacement for a Mega, with more I/O pins available, refer to the arm MBED F412ZG page.

The F446ZE has the same large footprint, however it has a significantly faster CPU and a USB OTG port. Refer to the arm MBED F446ZE page.

The F429ZI has the same large footprint, however it has the added benefit of onboard Ethernet, which makes it potentially suitable for larger or exhibition layouts where the WiFi limitations of the ESP01 firmware come in to play. Note, however, that the Ethernet support for this board in EX‑CommandStation is currently not implemented. It too has a USB OTG port. Refer to the arm MBED F429ZI page.


While the F429ZI is supported by the Arduino IDE, the F412ZG and F446ZE cannot be selected as build targets from within the Arduino IDE at present, and you will need to request the variant files and get some support from the DCC-EX dev team via Discord. The plan is to submit the F412ZG and F446ZE variant files to the STM32duino GitHub repo for inclusion once they are validated and debugged.

Upgrade the debugger firmware

During testing, it was noted with certain USB chipsets on Windows 11 that serial responses via the USB debugger port would stop being received by the serial monitor, even though the device continued to operate normally. The recommendation to resolve this issue is to upgrade the debugger firmware.

We recommend you upgrade the debugger firmware regardless if you experience this issue or not.

You need to ensure your NUCLEO device is plugged in to a USB port prior to commencing the upgrade.

In the same zip file as the drivers, you will need to navigate through the “en.stsw-link007_v3-10-3” folder down to the “Windows” folder, which contains an executable “ST-LinkUpgrade.exe” to upgrade the firmware on the NUCLEO devices.

Drivers installed

Double click this file to run it, which should present the upgrade window.

Drivers installed

Clicking the “Device Connect” button will attempt to connect to your NUCLEO device and display the currently installed firmware version, along with the version it will attempt to upgrade to.

Drivers installed

Providing your NUCLEO device has been detected and is running an older version of the firmware, click “Yex >>>>” to proceed with the upgrade.

Drivers installed

Hopefully you will see the “Upgrade is successful” pop up appear when complete.

Drivers installed

At this point, after clicking “OK” the software should display the new version of the firmware that has been applied to your device.

Drivers installed

Adding NUCLEO support to the Arduino IDE

In order to compile for the STM32 NUCLEO platforms, you will need to add the boards to the Arduino IDE.

To do this, navigate to “File” -> “Preferences” and add this URL to the “Additional Boards Manager URLs” list:


Arduino IDE Preferences

You will then need to navigate to “Tools” -> “Board” -> “Boards Manager”, search for “stm32”, and install the support for these boards.

Arduino STM32 board install

Once this has been performed, the NUCLEO devices should be available to be selected in the Arduino IDE.

Adding NUCLEO support to VS Code/PlatformIO

In order to compile for the STM32 NUCLEO platforms you need do nothing when using Microsoft VS Code and PlatformIO. PlatformIO will automatically download the required tool chains and frameworks for platform support based on the entries in platformio.ini inclued in the EX‑CommandStation source tree.

Just select “Nucleo-F411RE” or “Nucleo-F446RE” as the build target, and hit build. Be sure to do this after installing the drivers (for Windows) and upgrading the debugger firmware per the instructions above.

Hardware setup notes for a NUCLEO EX‑CommandStation

Here is how the NUCLEO-F411RE looks when new, with a top view, and the pinouts. The NUCLEO-F446RE board looks near identical, pinouts are exactly the same, however some of their I/O functions map slightly differently as the F411RE and F446RE microcontrollers are different internally.

STM Nucleo-F411RE top face STM Nucleo-F411RE connector pinouts

You will notice that the Ardiuno connectors are slightly inboard of the dual-row headers called the Morpho connectors.

Notes on the Arduino connectors on the NUCLEO range

  • Whilst the I/O pins are 5v-tolerant for digital IO, for the moment we recommend using 3v3 friendly Arduino R3 spec shields where you can.

  • The analog pins are NOT 5v-tolerant and accept a maximum of 3v3. We recommend using the genuine Ardiuno Motor Shield R3 revision (and only the R3!) for the moment. Instructions for modifying the earlier R2 version and the Deek Robot Motor Shield will follow in due course.

  • By default the Rx/Tx Arduino pins (D0/D1) are NOT connected to any of the NUCLEO’s pins. There are jumpers underneath to connect them to Serial2, but this isn’t recommended (see steps for serial connection below)

  • The Morpho pins extend both above AND below the Nucleo-64 series boards! Please be very wary of shorting any of these pins, especially those that protrude below. We recommend mounting 10mm M3 screw hex standoffs into the 3 mounting holes on the main PCB for your safety. See pic here:

STM Nucleo-F411RE underneath face with 10mm M3 standoffs

Here is the NUCLEO-F411RE with a genuine Arduino Motor Shield R3 installed:

STM Nucleo-F411RE with genuine Arduino Motor Shield R3 installed

Serial for WiFi, for F411RE and F446RE

The default serial port used for console communications for the F411RE and F446RE is Serial2, which has open solder pads to the Arduino Rx/Tx pins of D0/D1. Therefore there is no serial port connected to Arduino pins D0/D1 by default, and in any case we cannot use Serial2 for WiFi. As D0/D1 are completely unconnected, they do not interfere with any jumpers you install on a WiFi shield per the instructions below.

To connect an ESP8266 via either a WiFi shield or ESP01 module, you must use Serial1, which appears on different Morpho pins for the F411RE and F446RE.

The DCC-EX source code currently maps the Serial1 port pins to:

  • F411RE: Rx CN7 pin 17, Tx CN7 pin 21

  • F446RE: Rx CN10 pin 33, Tx CN10 pin 17

You will need to connect the Rx pin on your NUCLEO to the Tx pin of your WiFi device, and the Tx pin of the NUCLEO to the Rx pin of the WiFi device. Below are pics of the positions of each:

NUCLEO F411RE/F446RE Serial1 Rx/Tx Connections