STM32H745I-DISCO why is LD7 on and blinks?

[HTD]

On the board schematics the LED is just connected to PJ2.

I configured pin PJ2 as GPIO output push-pull, state high. So it should be off. But after roughly 1 second from reset the LED turns on and blinks like every 20 seconds.

It's supposed to be user LED, but I have no control over it's behavior. Well, when I tried to set PJ2 to H - it caused a blink during startup, that's all. It's even weirder, because looking at schematics it should blink when I set L, not H, knowing it's set to L most of the time.

[FBL]

Hi @Adam �?yskawa​ 

Could you please verify these points

1. Is there any signal on the pin PJ2 if you keep it input floating?
2. Is there any similar behavior for other user LEDs?

Make sure that unused pins are tied to ground or configured in analog mode

[HTD]

Ad 1 - Why? The problem is the pin is in low state, the signal is missing. I set it high, but it doesn't work. The LED is on when there's 0V on PJ2. So - something can short PJ2 - but it's not anything I connected to the board.

Ad 2 - No. LD6 works as expected, I can turn it on and off with no problem.

The unused pins are set up properly.

As I see on the schematics - PJ2 is also connected to the ethernet chip, however - this chip is not enabled and not initialized, so, at least in theory - it should not interfere. What's more weird, I tried to enable ETH device in CubeMX to see what pins it uses. PJ2 is not one of the pins used.

 

Well, it seems like pin 3 of the LAN chip makes LD7 useless... A bug in board design / documentation? Or ANOTHER bug in the firmware, so the unused LAN can be disabled not to short the pin 3, but it isn't?

[Mike_ST · Accepted solution]

Hello,

LD7 (with net name LED1) is not connected to LAN8740.

LED1/nINT/NPME/REGOFF is a pin name of the LAN8740 interface.

Maybe what you are seeing blinking is LD8, because if PD3 is kept floating (not configured) T5 is in undefined state and might toggle for no reason.

[HTD]

That makes sense, I have PD3 configured for SPI2 (I need it), so well, it will just blink then ;)