Minimum HCLK value for STM32F7?

[Abhishek Kumar]

Posted on January 09, 2018 at 13:50

I am working on STM32F777 where I see that cubeMX does not allows me to enter HCLK value below 16MHz.

1.) Is there a way to make it lower to something like 2 or 4MHz?

2.) How should I select clock frequencies to make the power consumption as low as possible?

3.)Does HCLK refers to the cpu core clock frequency?

#stm32f7 Note: this post was migrated and contained many threaded conversations, some content may be missing.

[Bogdan Golab]

Posted on January 09, 2018 at 16:14

Run CuneMX, enable HSE and play with frequency divider. I was able to have 0.310059MHz as HCLK (for mcu, memory). I guess this MCU do not have low frequency limitation - probably one of the gurus on this forum will correct me if I am wrong.

[Abhishek Kumar]

Posted on January 09, 2018 at 16:38

I did tried so, but when I try make HCLK go below 16MHz through dividers, cubeMX starts to show that in RED and marks as config error!

[Bogdan Golab]

Posted on January 09, 2018 at 17:03

Enter manually a valu e.g. 0.2 in the 'HCLK to ahb' and the divider will be set automatically

[Bogdan Golab]

Posted on January 09, 2018 at 17:04

Sometimes the app will ask you if you can accept different divider - press ok again

[Bogdan Golab]

Posted on January 09, 2018 at 17:05

So you have two ways of dowing things:

-selecting divider

OR

-entering the expected value and the system will do it for you (sometimes extra OK is required)

[Bogdan Golab]

Posted on January 09, 2018 at 17:08

[Abhishek Kumar]

Posted on January 09, 2018 at 21:58

Thanks for the help but I am still unable to enter this much low frequency value, see the message says:

[Bogdan Golab]

Posted on January 09, 2018 at 23:05

It seems the only difference is clock source - it automatically changed the source to HSI when I put 0.2MHz (it seems it is not possible for HSE)

[Tesla DeLorean]

Posted on January 10, 2018 at 01:39

The Datasheet says it can go from DC to 216 MHz, so I have no idea where this 2 MHz nonsense is coming from.

One could argue if peripherals will be usable at low frequencies