ST32F407VG MC01 and MC02 Prescalar Values

[oytuncakin]

Posted on February 26, 2015 at 00:15

Hi, I'm trying to understand and make some changes on to code already written.In clock configuration on this code MC01 and MC02 values have been changed to 2 and 5.Usually we were using them as default no division and don't know what their purposes.

Neither System Clock Configuration Exel nor the Clock Configuration Tree were enough usefull.Only clieve1 had mantioned about them on a topic [DEAD LINK /public/STe2ecommunities/mcu/Lists/cortex_mx_stm32/Flat.aspx?RootFolder=/public/STe2ecommunities/mcu/Lists/cortex_mx_stm32/STM32F4%20timer%20%28Prescaler%20Value%29&FolderCTID=0x01200200770978C69A1141439FE559EB459D7580009C4E14902C3CDE46A77F0FFD06506F5B&currentviews=7270]here.But couldnt understand much of it.Can any one please explane which clock signals they use, what purposes they are used for and which pins they have actually effect on in detail ?  #mc01-mc02-prescalar

[Tesla DeLorean]

Posted on February 26, 2015 at 01:00

Their function is described in the Reference Manual, you have prescalers because the maximum pin output speed is 84-90MHz, not the potential 168-180 MHz the PLL might allow.

The MCO pins allow the output of internal clocks signals, ie HSI (High Speed Internal - 16 MHz), HSE (High Speed External - whatever you supply), PLL (whatever you set them too). What they are used for in YOUR circuit is a whole other matter, a typical use case with Ethernet chips is to output a 25 MHz or 50 MHz to the MAC chip. On the ST-LINK they output a 8 MHz signal from the external crystal for use by the Target CPU. They do this because USB and CAN need high accuracy clocks, the HSI clock isn't stable or accurate, merely adequate for most applications.

[oytuncakin]

Posted on February 26, 2015 at 10:48

Thanks for the reply clive;

As like u said we managed to find them on referance manual on section 7.2.10 Clock-out capabilities.It's very usefull for us in the process of understanding this uncommented madness of code stack.