STM32G473 can't start debugging with incoming data stream on USART1 Rx pin

[Nabekaite]

On my board i use USART1 and USART3 to connect my device to other by dual RS-485. 485 tranciever connected to MCU throw digital isolator (4 tx, 2 rx SI8662). If 485 line of USART1 not connected ti device i can start debugging in Keil without problem. If i connect 485 line debug session immediately fail. If i connect line before debuging then i can't enter debug. Even ST-Link Utility can't connet to MCU with connected 485 line. I can load programm to MCU, connect 485 line an device will work fine by self. With 485 of USART3 no eny problem.

There is no galvanic connection between MCU and 485 tranciever, no ground connected. Power of both part of device is fine, no any noise.

Boot0 on MCU connected to GND. I use ST-Link v2 and SWD-connection.

Why debugging not work with incoming data stream on USART1?

[waclawek.jan]

Short between some of the SWD lines and RxD1?

What's the relationship between 3.3V of the silabs isolator, +5V from the DC/DC and the power supply to STM32?

When the RS485 line is unconnected, is the DC/DC powered down?

JW

[Nabekaite]

Nope. There is no any short between this lines.

[Nabekaite]

Here is how power is made in device

"When the RS485 line is unconnected, is the DC/DC powered down?" - no, DC/DC powered until device powered.

[waclawek.jan]

Then - if there's no problem with power supply, ground, conducted or radiated electromagnetic noise - the only change when the RS485 line is connected is the Rx signal, isn't it? So you problem must be related to it.

Disconnect the Rx signal (cut track, lift pin) and check.

JW

[Nabekaite]

I cut Rx track an Keil was able to load as much as 10% of the firmware.

Connection errors still here but i I think there are fewer of them.

[waclawek.jan]

Well, I don't know then, sorry.

JW

[TDK]

Make sure the SWD ground is the correct one. Lower SWD clock speed to try to help, but that won't fix the underlying problem. Seems like the problem isn't strictly the RX line.

[waclawek.jan]

Possibly related https://community.st.com/s/question/0D53W00000srAI6SAM/translating-incoming-data-from-pa10-usart1-rx-to-pb4-jtrst-with-erased-flash-or-under-reset-in-stm32g473

[Nabekaite]

Check SWD groung - ground is fine.

Try 400 kHz SWD speed - no change.

"Possibly related" - yes, it another my topic about my device.

[waclawek.jan]

The possible relationship to debugging is through the JTAG reset pin (NJTRST , PB4).

JW