STM32H755 HRTIM and USB multiplexing

[chrkaras]

Hello everyone,

I am using the NUCLEO-H755ZI-Q board for a project. I have noticed that the HRTIMs that

are not multiplexed with some USB pins (like the HRTIM_D1 with the D+ for programming the IC via usb)

work normally, while if they do, I can't output any PWM pulse. Is this actually a thing and to overcome it

I have to remove some of the Zero Ohm resistors behind the nucleo board or design a custom pcb for my needs

or am I messing something up? In my situation specifically, i can output from all HRTIM channels except the D1

and D2, both of which map to a pin with USB.

Thanks in advance! 

[FBL]

Hi @chrkaras 

Can you tell me which HRTIM outputs are you using ? Which resistors you removed?

[chrkaras]

Hi @FBL,

I tried using all HRTIM channels at once in the default pins that the cubemx assigns, and the only two that were not working are the D1 and D2 where both channels maps to the USB. I also had the same issue with the other channels when I reassigned them to other pins where there can be USB functionality. I DO NOT want to use the USB in my project, except when flashing the chip. Also I haven't disoldered any resistors. I am asking because I want to implement a custom board.

Thanks!

[Shirley.Ye]

what do you mean by D1, D2? could you please give out the GPIO port and pin?

[chrkaras]

HRTIM_CHD1 maps to PA11 pin and HRTIM_CHD2 to PA12. These pins also map to some USB functionality (USB_OTG_FS_DM and USB_OTG_FS_DP respectfully). While I do not use the USB, when I utilize the pins for the high resolution timer on the NUCLEO board (NUCLEO-H755ZIT6-Q specifically) for a standard pwm output it does not output anything while HRTIM_CHA1 or CHA2 that map on PC6 and PC7 do.

And let me generalize it, since I tried on purpose all different pins that have a timer (simple or from the high resolution) and USB multiplexed either as input or output; If a timer maps to a pin which also has some USB functionality, the timer does not work. I am always talking about the NUCLEO board I bought "out of the shelf". I haven't done any custom modifications. Don't get me wrong.

My questions; Is this happening because the nucleo board has the user USB multiplexed with the HRTIM CHD1 and CHD2 and that introduces parasitic phenomena? Is it because there are some SB connections underneath the board that reroute the output to the user USB?

Thanks for your patience.

[FBL · Accepted solution]

Hi @chrkaras 

PA11 / PA12 are USB OTG FS DM/DP pins. They are also available as HRTIM_CHD1 / HRTIM_CHD2 alternate functions.

So, on the Nucleo board, those pins are part of the USB routing. You need to redirect them manually. Checking board user manual, you need to set SB26 SB27 OFF; Then you can reuse them.