CLKOUT feature on STM32F205

[aamirali641989]

Posted on June 17, 2013 at 11:01

I have used following code to get CLKout on PC9 but it didn't work:

Sysyteminit() was called earlier.     /*Enable or disable the AHB1 peripheral clock */ RCC_AHB1PeriphClockCmd(RCC_AHB1Periph_GPIOC, ENABLE); /*Configure GPIO pin alternate function */ GPIO_PinAFConfig(GPIOC, GPIO_PinSource9, GPIO_AF_MCO);

[Amel NASRI]

Posted on June 17, 2013 at 11:43

Hello A2,

You have to configure the pin in AF mode then select the clock to be outpout:

/* Enable the GPIOC peripheral */
RCC_AHB1PeriphClockCmd(RCC_AHB1Periph_GPIOC, ENABLE); 
/*Configure MCO2 pin(PC9) in alternate function mode */
GPIO_InitStructure.GPIO_Pin = GPIO_Pin_9; 
GPIO_InitStructure.GPIO_Speed = GPIO_Speed_100MHz; 
GPIO_InitStructure.GPIO_Mode = GPIO_Mode_AF; 
GPIO_InitStructure.GPIO_OType = GPIO_OType_PP; 
GPIO_InitStructure.GPIO_PuPd = GPIO_PuPd_UP; 
GPIO_Init(GPIOC, GPIO_InitStructure); 
GPIO_PinAFConfig(GPIOC, GPIO_PinSource9, GPIO_AF_MCO); 
/* Select to output the SYSCLK */
RCC_MCO2Config(RCC_MCO2Source_SYSCLK, RCC_MCO2Div_1);

ST.MCU

[aamirali641989]

Posted on June 17, 2013 at 12:11

Thanks , it solved the problem. Also when I limit the GPIO freq by 100Mhz. but I set 120Mhz on MC02 & I was able to see it actually. How can this happen, Shouldn't it be limited to 100mhz

[Amel NASRI]

Posted on June 17, 2013 at 12:32

100MHz is the IO speed not the max system clock.

Even with less speed value, you should be able to output the SYSCLK, PLLCLK or HSE using the prescalers. Edit: You are right, for garanteed cases, the selected clock to output onto MCO must not exceed the maximum I/O speed. You can use the prescaler from 1 to 5 to get values greater than this speed (

RCC_MCO2Div_x

).

[Tesla DeLorean]

Posted on June 17, 2013 at 13:41

How can this happen, Shouldn't it be limited to 100mhz

It's a slew rate control setting, determining how hard/aggressively the pin is driven, it's external performance will be impacted by the capacitive load being driven. It is not a filter or physical limit in the sense you interpreted.