In order to program a target MCU with STLink you need to connect 4 wires – SWCLK, SWDIO, GND and VCC (3.3V). STLink v2 programmer has 3.3V pin already present and ready to use. But let's say I would like to use my STM32F401 Nucleo-64 development board as a programmer. In this case, I need to remove CN2 jumpers and use SWD connector. The problem is, SWD connector does not have target power (3.3V) pin. Where do I get 3.3V? Can I just take it from nucleo board?
Electronic – STLink 3.3V target power
nucleostst-link
Related Solutions
First of all, you are right, if your board has already got a supply voltage source you do not have to connect ST-Link's VDD pin.
The second thing I would recommend you is to open the STM32F411 Nucleo board's reference manual and look at the schematics. Especially the part where the ST-Link is connected to the controller on the board.
By ST Microelectronics, SWCLK, SWDIO, NRST and SWO (and GND of course) are connected to the target MCU. The additional SWO pin is used for debug purposes, you can access printed data with the printf function through this pin with ST-Link Utility.
The Printf via SWO Viewer displays the printf data sent from the target through SWO.
So I can recommend you to connect SWO as well, can be useful later. Connect your MCU to ST-Link just like they have connected the Nucleo's MCU to it.
As for boot configurations, there are three selectable options, easiest it to stick with the Main Flash and tie Boot0 to GND, but I do not know your requirements so it is up to you to choose.
I had the same problem! If you take a look at the PCB you see the NRST signal is messed up, meaning it is not connected to PB0 of the stm32F103 MCU in the programmer - instead it is connected to the "other side"(interestingly to a totally mirrored position of the MCU).
What I have done:
Removed the resistor R18 which connects the NRST connector pin to the wrong pin on the MCU. Then with a simple resistor 10R-100R I connected to NRST connector pin to the PB0 of the MCU (number 18 of the QFP 48).
After all, it woks just fine, for Trace support the SWO pin should be wired too You have to follow: https://lujji.github.io/blog/stlink-clone-trace/
Best Answer
Even an ST Link does not provide target power. You connect Vcc to power the level shifter in the ST Link. Such that the ST Link does not blow up an 1.8V target.
The budget version of the ST Link on the development boards do not offer this, and are only capable of interfacing with 3.3V targets. If your target is 3.3V, and not powered from elsewhere, you can connect 3.3V. If it is self-powered you can omit 3.3V.
I cannot find a board photo or circuit of the ST Link V2, but it will have some logic IC that provides level shifting/buffering between the STM32F103 (used in ST Link) and the target connector.
From the user manual of ST Link V2:
And the remark at the pinout table: