PLL Setting for USB CDC Question

[KNguyen]

Hi,

I trying to run the USB CDC Example but the PC does not recognize the USB.

I think it is the PLL Setting for the clock and I not sure how to set it up.

Can some one help.

My hardware use a 12MHz for the HSE and STM32105VC.

// Configure PPL Clock

oscinitstruct.OscillatorType = RCC_OSCILLATORTYPE_HSE; // Select HSE as Oscillator (12MHz input)

oscinitstruct.HSEState = RCC_HSE_ON; // Enable the HSE block

oscinitstruct.PLL2.HSEPrediv2Value = RCC_HSE_PREDIV2_DIV3; // Divide by 3 => 4MHz

oscinitstruct.PLL2.PLL2MUL = RCC_PLL2_MUL10; // Multiply by 10 => 40MHz

oscinitstruct.PLL2.PLL2State = RCC_PLL2_ON; // Enable the PLL2 block

oscinitstruct.Prediv1Source = RCC_PREDIV1_SOURCE_PLL2; // Select PLL2 (40MHz)

oscinitstruct.HSEPredivValue = RCC_HSE_PREDIV_DIV5; // Divide by PPL2 by 5 => 8MHz

oscinitstruct.PLL.PLLSource = RCC_PLLSOURCE_HSE; // as clock source the PLL block

oscinitstruct.PLL.PLLState = RCC_PLL_ON; // Enable the PLL block

oscinitstruct.PLL.PLLMUL = RCC_PLL_MUL9; // Multiply by 9 => 72MHz

HAL_RCC_OscConfig(&oscinitstruct);

/* USB clock selection */

rccperiphclkinit.PeriphClockSelection = RCC_PERIPHCLK_USB; // Set USB clock to

rccperiphclkinit.UsbClockSelection = RCC_USBPLLCLK_DIV3; // 72 x2 /3 = 48MHz

HAL_RCCEx_PeriphCLKConfig(&rccperiphclkinit);

The question is what clock the USB need? I thought the USB uses a 480MHz clock.

Thanks.

 

• This topic was modified 8 years, 9 months ago by support.

[support]

Hi,

Normally the USB clock needs to be 48 MHz. Please use the STM32CubeMX tool to validate your clock parameters:

You can read here about integrating code generated by STM32CubeMX into VisualGDB projects.

 

[Author]

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