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Question about flashing through the STDC14 connector

Associate III

Hey guys.

I'm trying to build a custom Pcb that doesn't include the onboard st-link and be able to program it though the STDC14 connector.

I found some schematics about the nucleo H7A3ZI-Q board, but i was confused about a couple of things.
1) The STDC14 connector uses the T_SWDIO and T_SWCLK pins. Do these pins go through the onboard st-link before reaching the processor?

2) What pins on the processor does the swi correspond to? Does it use the same pins as the default usart interface?

3) Would it be easier to flash the onboard processor if i used the CN2 Header? ( swd interface) Do these pins go through the on-board st link first, before reaching the processor?

ST Employee

Hello @AlexandrosAA 

I'm referring to MB1363-H7A3ZIQ schematic at page 9 STLINK_V3E.

If you want to implement a STDC14 connector on your own pcb:

1) The signals from STDC14, T_SWDIO and T_SWCLK  must be connected to PA13 and PA14 respectively.

2) I don't see any reference of swi? do you mean SWO instead?
If so it must be connected to PB3 for the Serial Wire Output.

3) On Nucleo-H7A3ZIQ, CM2 connector is reserved for STLINK_V3E onboard. It is not used to flash or program the STM32H7A3ZIT6QU device.

I hope it clarify your question?

Best regards,



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1) Do i just need to connect T_SWDIO and T_SWCLK to their respective pins and provide enough power to the board, so that i can flash the program, or do i need to do something else too?

2) Sorry, i was referring to it as serial wire interface.

3) SO there is no need to use that header, since the pins will be directly connected to the processor.


T_SWDIO and T_SWCLK need to go to the Target's SWDIO / SWCLK pins.

T_VCC should be coming from the Target's MCU power, to have SWDIO/SWCLK at the right voltage.

SWO would be helpful for SWV/TRACE operation

NRST is also strongly advisable, as it allows for "Connect Under Reset", which is a more aggressive connection / recovery method.

A switch or jumper for BOOT0, to a pull up or down resistor can also be helpful in recovering "bricked" devices.

A prevailing reason to use STDC14 over ARM's 10-pin configuration would be the VCP/UART connectivity

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So if got this right

T_SWDIO  should go from the stlink vset to pin PA13 on  the processor,

T_SWCLK should go from the stlink vset to pin PA14 on  the processor,

T_VCC should go from the processor's power source to the stlink,

T_NRST should go from the stlink vset to pin 27 on  the processor,