To use USB port of the mini STM32 v3. We need to configure the USB port and for that, we have to look at the schematics.
You can view the Full schematic here https://www.exasub.com/development-kit/mini-stm32-v3-0/mini-stm32-v3-0/
From the schematics, we see that there are three pins associated with the USB port.
1. PA11
2. PA12
3. PD2
The Pins PA11 and PA12 are
PA11 – USB D-
PA12 – USB D+
These two pins will be configured by the stm32cube ide when you enable the USB device.
PD2 should be configured as GPIO pin.
Because the USB FS implementation says to pull up the D+ line to 3.3V.
The pull up is performed by the S8550 PNP transistor.
So by making the PD2 pin LOW, we enable the USB FS, since it makes the D+ pull up.
We also need to select the Communication Device Class as Class For FS IP.
After configuring the cube mx project. we can proceed to generate code.
The code needs to add the following header file
/* USER CODE BEGIN Includes */
#include "usbd_cdc_if.h"
#include "string.h"
/* USER CODE END Includes */and then in the main() function. you can write this code in while loop
/* USER CODE BEGIN 2 */
HAL_GPIO_WritePin(GPIOD, GPIO_PIN_2, GPIO_PIN_RESET);
/* USER CODE END 2 */
/* USER CODE BEGIN WHILE */
uint8_t *data = "Hello World from USB CDC\r\n";
while (1)
{
CDC_Transmit_FS(data, strlen(data));
HAL_Delay (1000);
/* USER CODE END WHILE */
/* USER CODE BEGIN 3 */
}
/* USER CODE END 3 */
After uploading the code to your microcontroller. It will be displayed in your windows device manager as “USB Serial Device”.
You can Connect to the Com port using the serial terminal software such as YAT, Putty or CoolTerm etc.
Note: Since it is a virtual com port, you dont have to set a specific baud rate.
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