Schematic to connect STLink-V3MINIE to STM32 MCU

[DSebastian]

Hi,

after starting with Nucleo-L432KC development board I need to switch to a variant with more I/Os, and thus I’m creating a stand-alone development board with STM32L462CET in LQFP48 package.

I purchased a STLink-V3MINIE for programming/debugging but, like others, was confused on how to properly connect the STLink to the MCU. Since various answers are given in lots of threads I summarized in a simplified sketch what I consider as correct.

Please have a look on attached schematic and configuration of MCU done in CubeMX. To keep it as simple as possible I removed everything but the MCU, the STDC14 connector of the V3MINIE and just an LED to apply the minimum blink-example.

Please, focus on the connection of STDC14 connector and BOOT0. I think, with this, it is possible to download the blink-software and run the debugger. Am I correct?

Regards

Sebastian

 

[David Littell]

Not connecting NRST to a proper circuit (i.e., not just a pushbutton and a cap - and where’s the pull-up?) on the MCU side is always a mistake.

[DSebastian]

Hm,

yes, it looks strange, but actually it follows reference design given in AN4555 (provided for LQFP144 package), and no contradiction to datasheet of the MCU (see attached figures). R_PU is specified as typical 40k.

I can make the NRST pin accessible for the breakout board, but there are no further details given how the pull-up shall be modified.

 

[TDK]

Yes, this is correct and will let you program the chip. Power needs supplied externally, seems like that’s what you’re doing.

If R1, R2, R3 aren’t installed, those lines won’t work. Schematic is unclear if these are DNI components or 0 ohm resistors. Seem like DNI. But you don’t need them to program. NRST can be nice to have connected if you’re using low power modes.

[DSebastian]

Ok, schematic about R1, R2, and R3 is a little misleading. I was trying to point out that such are resistors are not needed while overlooking that the symbol actually says DNI leaving the connection to STDC14 connector open.

So it shall be like this (yes, external power supply):

 

The hint with regards to NRST and low power modes I didn’t understand. Can you rephrase, please?

[Andrew Neil]

The hint with regards to NRST and low power modes I didn’t understand. Can you rephrase, please?

If the CPU is asleep and/or you reconfigure the SWD pins, then you won’t be able to connect via SWD.

Being able to assert NRST will get you out of this.