Why do we have 2 connectors namely CN2 (SWD) and CN3 (ST-LINK) on STM32F407 Discovery board? Are not they the same thing?enter image description here


1 Answer 1


No, they're not the same.

The pair of jumpers on CN3 connects the ST-Link to the target device (i.e, the STM32F407 located on the Discovery board).

When those jumpers are removed, the SWD pins on CN1 can be used to connect the ST-Link to another target device.

  • \$\begingroup\$ ok i got it now. If i have to make my custom pcb using STM32F407 MCU then which connector should i use in it to flash the mcu.. CN2 or CN3? \$\endgroup\$
    – scico111
    Commented Feb 9, 2019 at 0:34
  • \$\begingroup\$ If i don't want to use the on-board ST-Link circuit of this discovery board but instead i want to use a ST-Link device to flash the on-board 'F407 MCU then how would that be possible? \$\endgroup\$
    – scico111
    Commented Feb 9, 2019 at 0:46
  • 1
    \$\begingroup\$ 1) Use CN2 to connect the onboard ST-Link to other devices. CN3 is only for jumpers. 2) Connect the external ST-Link to the appropriate pins on the MCU headers (P1 and P2). \$\endgroup\$
    – user39382
    Commented Feb 9, 2019 at 2:54

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