A short guide to choosing PWM pins for your application

When it comes to choosing pins for your application, there are a few things to consider. The most important thing is to make sure that the pins you choose are compatible with the hardware you are using. Make sure to check that your microcontroller family and SimpleFOC supports the necessary PWM generation, position sensor and current sensing technique. You can find this info in our docs here.

Once you are sure that you microcontroller is apt to the application, it is time to consider which pins to use. There are three main questions:

1. Which pins to use for PWM generation?
2. Which pins to use for the position sensor?
3. Which pins to use for current sensing?

In this guide we will focus on the first question: Which pins to use for PWM generation?

The answer to these questions depends on the microcontroller you are using and the hardware you have. Here is the list of microcontroller families supported by SimpleFOC and the PWM generation modes supported by each of them:

What is important to see is that all the supported families can be used with 2/3/4PWM modes. However, not all the architectures support 6PWM mode. Additionally, the PWM frequency can be configured for all the supported architectures, but for Arduino AVR boards, the frequency can be set to either 4kHz or 32kHz.

Another important factor when it comes to choosing the PWM pins is to try to use the PWM pins that belong to the same timer. This is important because the PWM signals generated by the pins that belong to the same timer will have the same frequency and phase. This is important for the FOC algorithm to work properly. The rule of thumb:

• For 2PWM mode, try using only one timer.
• For 3PWM mode, try using only one timer.
• For 4PWM mode, try using only one timer if possible, if not use one timer per phase (so two timers).
• For 6PWM mode, try using only one timer if possible, if not use one timer per phase (so three timers).

SimpleFOC does synchronise the PWM signals generated by different timers in some cases (as shown on the table above), but it is always better to use the pins that belong to the same timer.

The information about the timers associated with the pins is sometimes hard to obtain, especially for less experienced users. So in the next few sections we will provide some information on how to find the PWM pins for some of the most popular microcontroller families.

• Arduino AVR boards
• ESP32 boards
• STM32 boards
• Teensy boards

Arduino AVR boards

For Arduino AVR boards (UNO, MEGA, Nano, Leonardo, …), the PWM pins are usually marked with a ~ sign. These pins are the ones that can generate PWM signals. If you are writing an application with 2PWM,3PWM or 4PWM modes, you can use any of the PWM pins. The PWM timers are mutually synchronised so you do not have to worry about this info.

However if you are using 6PWM mode, you will have to use the pins that belong to the same timer. The pins that belong to the same timer are:

So if using one of these boards with 6PWM make sure to use the High/Low pair of pins that belong to the same timer. So in that case atmega328P and atmega32u4 have to use all of their PWM pins to generate 6PWM signals (atmega32u4 cannot use the pin 5 as it is alone on the timer TIM3). Also, atmega2560 has enough pins to run two 6PWM drivers using only one timer.

ESP32 boards

Esp32 boards have two PWM generation modules: LEDC and MCPWM. The LEDC module is used for generating PWM signals for LEDs, but it can also be used for motor control. The MCPWM module is specifically designed for motor control.

MCPWM module

So when using esp32 boards that have MCPWM module (ex. esp32 and esp32s3) you can use any of the pins for any form of PWM generation. This module allows the esp32 to be very flexible and allows for any pin to be used in PWM mode as well as to be associated to any timer. Typically, esp32 boards have 2 MCPWM independent modules allowing to instantiate:

• 4 instances of 2PWM mode drivers
• 4 instances of 3PWM mode drivers
• 2 instances of 4PWM mode drivers
• 2 instances of 6PWM mode drivers

This association of the appropriate timer and chanel for your applications will be done automatically by the SimpleFOC.

All the esp32 architecture that have the MCPWM will by default use MCPWM for motor control.

LEDC module

However, if using the boards that only support the LEDC module (ex. esp32s2 and esp32c3), you will not be able to use the 6PWM mode. You will still be able to use 2PWM, 3PWM and 4PWM modes. LEDC times usually have 8 channels and different boards have different number of channels and timers available. All the pins can be used for PWM generation, but first 8 pins are associated with the first timer, the next 8 pins with the second timer and so on.

Here is the list of the number of channels available for different esp32 chips, taken from the esp32 technical reference manual:

If the user wants to force using the LEDC driver for the boards that support MCPRM he has to set the SIMPLEFOC_ESP32_USELEDC.

STM32 boards

Stm32 is the most powerful family of microcontrollers supported by SimpleFOC, at least in terms of motor control capabilities. SimpleFOC supports most of the STM32 boards and all of them can be used in 6PWM mode. Additionally from the release v2.3.3 the SimpleFOC library synchronises the PWM signals generated by different timers by default. Therefore for all the use cases except 6PWM generation, the user does not have to worry about the timers associated with the pins, however it is still recommended to use the pins that belong to the same timers.

When it comes to 6PWM mode, the user has two choices:

1. Use the pins that belong to the same timer. This is the recommended as all stm32 boards have timers typically TIM1 and TIM8 that are desigened for this applications and allow for the best performance.
2. Use one timer per phase. This is also a goof solution, especially if the pins necessary to use the advanced timers are not available. However, in this case the application uses 2 or 3 timers instead of 1 which might reduce the capacity of the microcontroller to do other tasks in parallel.

Once you provide the SimpleFOC driver object with a set of pins, the library will automatically associate the pins with the appropriate timers and channels and find the best combination for motor control. If the pins are not compatible with the motor control mode you are trying to use, the library will throw as error.

Finding the pins that belong to the same timer is not an easy task, especially for less experienced users. Therefore, we’ve created a website that enables a realtively easy navigation of the pins and timers for the most popular stm32 boards.

Open stm32 pinout helper

As a rule of thumb, most of the stm32 boards have following pins that belong to the advanced timer TIM1:

• PA8 - channel 1
• PA9 - channel 2
• PA10 - channel 3
• PB13 - inverted channel 1N
• PB14 - inverted channel 2N
• PB15 - inverted channel 3N

So this is the combination of pins that is preferred for 6PWM mode.

Teensy boards

Teensy boards are very powerful and have a lot of timers that can be used for PWM generation. The SimpleFOC library supports all the Teensy3 and Teensy4 boards and all of them can be used in 6PWM mode.

Here is the table taken from teensy docs listing the PWM pins of different teensy families:

SimpleFOC does not synchronise the PWM signals generated by different timers for Teensy boards, so it is recommended to use the pins that belong to the same timer.

Teensy3

So when using Teensy3 boards, it is recommended (not a hard constraint) to use the pins that belong to the same timer. The pins that belong to the same timer are listed in the tables below.

All Teensy3 boards can be used in 6PWM mode on timer FTM0, and the ones that have FTM3 have the possibility to use 6PWM mode on FTM3 as well. SimpleFOC does not allow for other combinations of timers for 6PWM mode, at least till the release v2.3.3

Teensy4

When using Teensy4 boards, it is recommended (not a hard constraint) to use the pins that belong to the same timer. The pins that belong to the same timer are listed in the tables below.

Teensy4 has a combination of two timer types FlexPWM and QuadTimer. For 2PWM, 3PWM and 4PWM modes you can use any of the pins listed above, even if they belong to a combination of QuadTimer and FlexTimer channels. However, for best results, it is recommended to use the pins that belong to the same timer, or at least one timer per phase. Especially since SimpleFOC library, as of release v2.3.3 does not by default synchronise the PWM signals generated by different timers for 2PWM, 3PWM and 4PWM modes. Additionally, the generated PWM signals are not center-aligned either.

SimpleFOC, by default, does the center-alignment and timer sync only for 6PWM drivers. If you want to force the center-aligned 3PWM mode on Teensy4, you can set the SIMPLEFOC_TEENSY4_FORCE_CENTER_ALIGNED_3PWM flag. This will force the center-aligned 3PWM mode and sync the timers if using multiple ones. However, both of these modes require using FlexPWM timers and cannot be used with QuadTimer timers.

6PWM

SimpleFOC as of the release v2.3.3 allows for 6PWM mode only on FlexPWM timers. The pins that belong to QuadTimer timers are not supported for 6PWM. Additionally, SimpleFOC requires to use one submodule per phase of the 6PWM mode, if that is not the case, SimpleFOC will show an error. In order to use the 6PWM, for each phase, chose the pins A and B from the same time and submodule. The pin X is not used in the 6PWM mode.

Center-aligned 3PWM

If you want to force the center-aligned 3PWM mode on Teensy4, you can set the SIMPLEFOC_TEENSY4_FORCE_CENTER_ALIGNED_3PWM flag. For this mode you can use any of the pins A, B or X that belong to any the FlexPWM timers. SimpleFOC will automatically sync the timers if using multiple ones. If application allows it, it is recommended to use channels A and B of timers and avoid X. Additionally, if the flag is set and you try to use a QuadTimer timer, SimpleFOC will show an error.

Here is the table showing the pins A, B and X for each timer and submodule.