DFU USB and USART are not getting in some boards

[PKuma.0]

Dear ST Team

We are using STM32F765IGT6 in our design in a lot of 10 cards ,6 cards are not able to detect DFU and USART1/3 in boot mode.

After programming they are giving proper console at USART 1 as per my design.

Kindly suggest some debugging steps for getting DFU and USART1,/3 at boot mode

[Tesla DeLorean]

Make sure BOOT0 is pulled high adequately

Make sure your reset circuit behaves consistently with the rise of the power supply.

Scope NRST, BOOT0 and supply at start up.

Review potential for noise on other pins the boot-loader is watching (AN2606)

For USB make sure external clock starts properly and quickly.

The USART connectivity watches for the 0x7F pattern, and responds with 0x79. This is a one shot deal. Observe with a scope and have your test fixture / programming station be capable of resetting and retrying if initial connectivity fails.

[PKuma.0]

Hi Clive

Thanks for your suggestions and we perform above all steps :

1)We are using 4.7K pull up resistor at 3.3 V

2)Power on reset is working properly and send good signal after 250ms when 3.3V reached at 3.0 V

3)We have scope NRST and Supply at start up it's fine ,But is there any relation to BOOT0 pin with NRST???????????

4)For USB make sure external clock starts properly and quickly >> Please tell some more details about this

Clive , All boards are same so how,s it possible that some cards are working pretty good (Means DFU USB and USART1 ) and some are not having anyone interface , is there any possible mistake at micro controller side .

[Tesla DeLorean]

>> is there any possible mistake at micro controller side .

Unlikely to be that convenient, you could check the date code and loader firmware versions to see if they differ.

>>All boards are same so how,s it possible that some cards are working pretty good

They are built with different component, and may have soldering issues, or components which are marginal. The boards behave differently, so assume there are differences, and the task is to identify what those are.

>>But is there any relation to BOOT0 pin with NRST???????????

It samples BOOT0 at reset?

>>Please tell some more details about this

From your own code quantify the startup time of the external oscillators. Route signals via PA8/MCO so you can inspect without loading the circuits. Check stability, frequency, etc.