Nucleo-H743ZI2: if the HSE bypass mode still active when the board is powered by 3V3_EXT?

[Jiaming]

Hello,

I want to confirm on the Nucleo-H743ZI2 board, that if the HSE bypass mode is still active (can be used) when I power the board by the 3V3_EXT? I checked the manual UM2407, and it said the Debug chip will not work when the board is powered by 3V3_EXT. And I know the HSE bypass clock come from the MCO of the debug chip. So if the debug chip does not work, the HSE bypass clock source will also not be available as MCO does not function, right? Thanks in advance.

[AScha.3 · Accepted solution]

Hi,

If you dont give power to debug cpu, it will also not generate the clock (used in bypass mode on H743).

So you have some ways to go :

- give 3v3 to the debug cpu (even if no usb connected for using debug), just to do the clock output.

- remove SB to debug cpu and use local crystal on H743 (some boards have, some not - look whats on your board.)

- use HSI on H743 , then no need for clock or crystal. (If dont need precision clock -- for USB, CAN etc.)

[SofLit]

Hello,

How are you sure there is a clock generated by the ST-Link block and not you are using HSI? Did you see a clock signal on STLK_MCO?