Nucleo Boards for Control Systems

To install STM32CubeIDE and to run a Hello World example, please check it here: http://wiki.robolabo.etsit.upm.es/index.php/Nucleo_Boards

GPIO read and write

Read from a GPIO

HAL_GPIO_ReadPin (GPIOA, GPIO_PIN_9);

Write to a GPIO

- High level:

HAL_GPIO_WritePin(GPIOA, GPIO_PIN_8, GPIO_PIN_SET);

- Low level:

HAL_GPIO_WritePin(GPIOA, GPIO_PIN_8, GPIO_PIN_RESET);

Encoder

Theory

The encoder used is a position sensor that uses a two-channel hall effect sensor. It is a quadrature encoder that is attached to the motor shaft and which provides a resolution of 48 counts per revolution. This means that for a complete turn of the motor shaft, the encoder provides a value of 48 counts. The hall sensor requires an input voltage and the output of the encoder comes from reading the output of the two channels, channel A and channel B. These two channels are square waves which are 90ª out of phase.

PWM

Main registers

Prescaler (PSC)

The prescaler is a register that divides the timer clock frequency to obtain a specific frequency. Specifically, the frequency reduction is applied using the following formula:

f_PWM = f_CLK / (PSC + 1)

Therefore, if the frequency to set is the same as the frequency of the clock, the PSC register must be set at PSC=0. The STM32 timers allow a prescaler value up to 65535, through 16 bits registers.

Auto Reload Register (ARR) and Capture Compare Register (CCR)

The ARR register storages the maximum value that the counter can reach before going back to zero. Moreover, the CCR registers the value of the corresponding timer counter after which the output PWM signal goes from high to low level. Every channel of the timer used to generate the PWM will have a different CCR register (for example, CCR1 and CCR2 for channels 1 and 2). In this way, the value of the CCR together with the value of the ARR define the width of the pulses and, therefore, the duty cycle of the PWM signal:

Duty_Cycle (%) = 100 * (CCR / ARR)

CNT

This is the register that storages the value of the counter used to generate the PWM.

PWM Configuration in STM32CubeIDE

To configure a timer as PWM, the first thing to do is to select one of the timers that could be configured as a PWM generator. Additionally, also the channels that will be used as PWM output must be decided.

Advice: As different PWM outputs are needed, it is recommended to use different channels of the same timer to the extent possible.

The main timers that can be set as PWM are: TIM2, TIM3, TIM4 and TIM5, with 4 different channels each of them.

Advice: It is recommended to use the timer and the corresponding channels that match directly with the pins that feed the H-bridge to modulate the speed of the motor. Otherwise, the PWM output signals must be bridged with the H-bridge input signals.

Therefore, the pins that the channels of the timer are using need to be checked in the "Pinout" section of the STM32CubeIDE.

Once the channels of the timer have been activated, some parameters and the configuration of the timer must be changed.

Main parameters:

• Clock Source: Clock of the timer. The Internal clock option must be selected. Moreover, it must be checked that the frequency of the clock that is being used is the one desired. This could be checked within the clock configuration tab of the STM32CubeIDE.
• Channel x: Configuration for the channel x of the timer. The option “PWM Generation CHx” must be selected, in which x will be the number of the channel to configure.
• Prescaler (PSC): Parameter to introduce the value of the PSC register.
• Counter Period: Parameter to set the value of the ARR register.
• Pulse (16 bits): Parameter to mofidy the CCR register.
• Mode: The PWM mode 1 must be selected.

Additionally, within the code, the timer to use must be initialized following the structure below:

HAL_TIM_PWM_Start(&htim3, TIM_CHANNEL_1);

The CCR value can be modified by introducing the following instruction:

htimx.Instance->CCR1 = new_ccr;

in which CCR1 indicates that we are accessing to the channel 1 register, new_ccr is the new to set and htimx refers to the timer x (for example, htim2 or htim3).

In the same way, to modify the register of the channel 2:

htimx.Instance->CCR2 = new_ccr;