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As I know, Virtual COM port of ST-Link connection is connected to Usart2 on a STM32F401Re. When, ST-Link part is still attached everything is working fine on Usart2.

However, after cutting ST-Link part of the PCB, I am trying to connect a USB-TTL converter to PA2/PA3 pins and it is not working.

Power is maintained by USB-TTL converter, therefore JP5 is settled to E5V. Power delivery is quite OK. However, I can not get TX-RX work. I also tried to close SB62 & SB63 bridge solders. Nothing changed.

How can I connect F401RE board using usart2 to PC without using VirtualCom supplied by ST-link? Thanks.

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  • \$\begingroup\$ SB61, SB62 and SB63 must be open. Unless you remove the ST Link, then 62 and 62 must be close. Use pins D1 and D0 on arduino header. \$\endgroup\$ – Jeroen3 Jun 18 at 11:19
  • \$\begingroup\$ So, how exactly is the USB-TTL converter connected to the board, which pin goes where? What kind of other components are connected to the board? \$\endgroup\$ – berendi Jun 18 at 11:49
  • \$\begingroup\$ "Not working" is not a sufficient problem statement for this site. You need to document exactly what happens - does the serial transmit line stay stuck high, or low? Or does it toggle but not appropriately? What about the receive side, does that work? What if you change the firmware and drive the signal as a GPIO, can you make them slowly toggle then? Likely guesses are either that you aren't using the hardware the way you think you are, or much less likely that the trace got shorted to an internal plane when you broke off the programmer portion of the board. \$\endgroup\$ – Chris Stratton Jun 18 at 14:21
  • \$\begingroup\$ I already tried Jeroen3's suggestion. Not working. For the Berendi's question, I connected USB-TTL converter's pins accordingly: 5V->CN/ e5V, GND-> CN7 GND, TX->CN9 RX, RX->CN9 TX. Also, tried PA2, PA3 with SB61, SB63 closed and opened. \$\endgroup\$ – Sefer Bora Lisesivdin Jun 19 at 6:49
  • \$\begingroup\$ Dear Chris Stratton, I am sorry for I can not give any other details on the serial connection's health. \$\endgroup\$ – Sefer Bora Lisesivdin Jun 19 at 6:52

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